BUG: use entire size of DatetimeTZBlock when coercing result (#15855)
 - [x] closes #15855 
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=h1) Report
> Merging [#15924](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4502e82083f4e253630588665a4fc6002c4f32ed?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15924/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #15924      +/-   ##
==========================================
- Coverage   90.96%   90.96%   -0.01%     
==========================================
  Files         145      145              
  Lines       49557    49557              
==========================================
- Hits        45081    45079       -2     
- Misses       4476     4478       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.72% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.61% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `93.54% <100%> (-0.08%)` | :arrow_down: |
| [pandas/tseries/index.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvaW5kZXgucHk=) | `95.33% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=footer). Last update [4502e82...35912e1](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=h1) Report
> Merging [#15924](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4502e82083f4e253630588665a4fc6002c4f32ed?src=pr&el=desc) will **increase** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15924/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #15924      +/-   ##
==========================================
+ Coverage   90.96%   90.98%   +0.01%     
==========================================
  Files         145      145              
  Lines       49557    49521      -36     
==========================================
- Hits        45081    45058      -23     
+ Misses       4476     4463      -13
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.61% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `93.54% <100%> (-0.08%)` | :arrow_down: |
| [pandas/types/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL3R5cGVzL2NvbW1vbi5weQ==) | `93.64% <0%> (-0.3%)` | :arrow_down: |
| [pandas/tseries/index.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvaW5kZXgucHk=) | `95.33% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.89% <0%> (-0.08%)` | :arrow_down: |
| [pandas/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2luZGV4ZXMvYmFzZS5weQ==) | `96.09% <0%> (-0.06%)` | :arrow_down: |
| [pandas/core/reshape.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS5weQ==) | `99.27% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.57% <0%> (ø)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `93.06% <0%> (ø)` | :arrow_up: |
| [pandas/core/sorting.py](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc29ydGluZy5weQ==) | `97.81% <0%> (+0.03%)` | :arrow_up: |
| ... and [4 more](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=footer). Last update [4502e82...431b630](https://codecov.io/gh/pandas-dev/pandas/pull/15924?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). thank you sir!