 BUG: Correctly weekly resample over DST
- [x] closes #21459
- [x] closes #9119
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @mroeschke! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/resample.py`](https://github.com/mroeschke/pandas/blob/e23fcd9068c522c8862f5090a6738c20a359dbd5/pandas/core/resample.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_resample.py`](https://github.com/mroeschke/pandas/blob/e23fcd9068c522c8862f5090a6738c20a359dbd5/pandas/tests/test_resample.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22941?src=pr&el=h1) Report
> Merging [#22941](https://codecov.io/gh/pandas-dev/pandas/pull/22941?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9caf04836ad34ca17da7b86ba7120cca58ce142a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22941/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22941?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22941      +/-   ##
==========================================
+ Coverage   92.19%   92.19%   +<.01%     
==========================================
  Files         169      169              
  Lines       50822    50824       +2     
==========================================
+ Hits        46855    46858       +3     
+ Misses       3967     3966       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <100%> (ø)` | :arrow_up: |
| #single | `42.36% <16.66%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22941?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/22941/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.98% <100%> (+0.01%)` | :arrow_up: |
| [pandas/util/\_depr\_module.py](https://codecov.io/gh/pandas-dev/pandas/pull/22941/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlcHJfbW9kdWxlLnB5) | `67.44% <0%> (+2.32%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22941?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/22941?src=pr&el=footer). Last update [9caf048...bf1ddd5](https://codecov.io/gh/pandas-dev/pandas/pull/22941?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks @jreback !