BUG: Switch more size_t references to int64_t
closes #20785

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

While I agree with @jeffknupp's comment in #17063 that we should really be using `size_t` for these types, this patch switches some `size_t` that were switched from `int` in https://github.com/pandas-dev/pandas/commit/d5c75e8e8456c6e84bf6905eeedba92b1d369330 and not subsequently switched to `int64_t` in https://github.com/pandas-dev/pandas/commit/e04d12a9735707927edebf20501c1176ef5a2859 or https://github.com/pandas-dev/pandas/commit/3171674567c90aaaf7b723e2cc72c418ce374d18 This patch seems to fix the issue on 32-bit big-endian, I'm running some tests now to make sure it doesn't break anywhere else.
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20786?src=pr&el=h1) Report
> Merging [#20786](https://codecov.io/gh/pandas-dev/pandas/pull/20786?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4de2e9bc0d0a7a20232b4c41e2e5861c14bcf4b2?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20786/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20786?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #20786   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files         153      153           
  Lines       49305    49305           
=======================================
  Hits        45286    45286           
  Misses       4019     4019
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.24% <ø> (ø)` | :arrow_up: |
| #single | `41.89% <ø> (ø)` | :arrow_up: |


------

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 All tests OK on this side, and I added a whatsnew note. look good. ping on green. ping thanks @ginggs 