Consistent Timedelta Writing for all Excel Engines
- [X] closes #19900
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

I've basically copied the implementation that was done for the `XlwtWriter` class in #19244 over to the other engine subclasses for an easy fix. This might also fix #19911
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19921?src=pr&el=h1) Report
> Merging [#19921](https://codecov.io/gh/pandas-dev/pandas/pull/19921?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/74dbfd0aa9b44936a4db7969bfe25f526fef53ce?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19921/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19921?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19921      +/-   ##
==========================================
- Coverage   91.68%   91.65%   -0.03%     
==========================================
  Files         150      150              
  Lines       48976    48976              
==========================================
- Hits        44903    44891      -12     
- Misses       4073     4085      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.03% <ø> (-0.03%)` | :arrow_down: |
| #single | `41.85% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19921?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19921/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/19921?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/19921?src=pr&el=footer). Last update [74dbfd0...3fd5187](https://codecov.io/gh/pandas-dev/pandas/pull/19921?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 The Travis failure is coming from `TestTSPlot.test_mixed_freq_regular_first` and does not appear related to the change made at all.  All green otherwise thanks @WillAyd nice patch! does this close #19911 ?