Fix incorrect exception raised by Series[datetime64] + int
Series[datetime64] +/- int is currently raising a ValueError when it should be raising a TypeError.  This was introduced in #19024.

In the process of fixing this bug, this also goes most of the way towards fixing #19123 by raising on add/sub with integer arrays.

Setup:
```
dti = pd.date_range('2016-01-01', periods=2)
ser = pd.Series(dti)
```

ATM:
```
>>> ser + 1
[...]
ValueError: Cannot shift with no freq
```

After this PR (and also in 0.22.0 and anything before #19024):
```
>>> ser + 1
[...]
TypeError: incompatible type for a datetime/timedelta operation [__add__]
```

- [ ] closes #xxxx
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19147?src=pr&el=h1) Report
> Merging [#19147](https://codecov.io/gh/pandas-dev/pandas/pull/19147?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c271d4dd0b014c41bd91048fa6e8d33c5bf27b44?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19147/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/19147?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19147      +/-   ##
==========================================
- Coverage   91.56%   91.53%   -0.03%     
==========================================
  Files         148      148              
  Lines       48856    48870      +14     
==========================================
+ Hits        44733    44735       +2     
- Misses       4123     4135      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.91% <100%> (-0.03%)` | :arrow_down: |
| #single | `41.69% <55.55%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19147?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19147/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `92.17% <100%> (+0.1%)` | :arrow_up: |
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/19147/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `97.11% <100%> (+0.03%)` | :arrow_up: |
| [pandas/errors/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/19147/diff?src=pr&el=tree#diff-cGFuZGFzL2Vycm9ycy9fX2luaXRfXy5weQ==) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19147/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.22% <0%> (-1.74%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19147?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/19147?src=pr&el=footer). Last update [c271d4d...2231505](https://codecov.io/gh/pandas-dev/pandas/pull/19147?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Re-push or let sit? needs a rebase needs a rebase, otherwise lgtm. ping on green. Ping One more bugfix is ready to go once this goes in, plus another PR getting rid of _Op and _TimeOp. thanks!