fix(whl_library): actually apply patches and warn if RECORD file patch is needed

[aignas]

Before this PR there was a typo, that was actually causing the
patching function to not use the provided patches. With this change
we are finally correctly doing it. After fixing this bug I noticed
that repository_ctx.patch results in files with CRLF on Windows,
which made me make the RECORD mismatch to be a warning rather than
a hard failure to make the CI happy and allow users on Windows to
patch wheels but see a warning if they have a multi-platform bazel
setup.

The CRLF endings on Windows issue is fixed in
bazelbuild/bazel@07e0d31

Related #1631, #1639.

[aignas]

It seems that the tests started failing on windows, because bazel's rctx.patch has different behaviour on Windows as it is replacing the line endings with CRLF as opposed to leaving them LF.

I could reproduce this by changing the repackaging code with:

--- a/python/private/repack_whl.py
+++ b/python/private/repack_whl.py
@@ -148,6 +148,8 @@ def main(sys_argv):

         with _WhlFile(args.output, mode="w", distinfo_dir=distinfo_dir) as out:
             for p in _files_to_pack(patched_wheel_dir, record_contents):
+                if p.name == "METADATA":
+                    p.write_text(p.read_text().replace("\n", "\r\n"))
                 rel_path = p.relative_to(patched_wheel_dir)
                 out.add_file(str(rel_path), p)

And the test started failing with:

repack_whl: ERROR: Please also patch the RECORD file with:
--- a/requests-2.25.1.dist-info/RECORD
+++ b/requests-2.25.1.dist-info/RECORD
@@ -17,7 +17,7 @@
 requests/structures.py,sha256=msAtr9mq1JxHd-JRyiILfdFlpbJwvvFuP3rfUQT_QxE,3005
 requests/utils.py,sha256=_K9AgkN6efPe-a-zgZurXzds5PBC0CzDkyjAE2oCQFQ,30529
 requests-2.25.1.dist-info/LICENSE,sha256=CeipvOyAZxBGUsFoaFqwkx54aPnIKEtm9a5u2uXxEws,10142
-requests-2.25.1.dist-info/METADATA,sha256=fRSAA0u0Bi0heD4zYq91wdNUTJlbzhK6_iDOcRRNDx4,4177
+requests-2.25.1.dist-info/METADATA,sha256=FIRoD6JzkS0gW2tgRJemIR-Dj9FVZPLY7ALIWbib-bg,4280
 requests-2.25.1.dist-info/WHEEL,sha256=Z-nyYpwrcSqxfdux5Mbn_DQ525iP7J2DG3JgGvOYyTQ,110
 requests-2.25.1.dist-info/top_level.txt,sha256=fMSVmHfb5rbGOo6xv-O_tUX6j-WyixssE-SnwcDRxNQ,9
 requests-2.25.1.dist-info/RECORD,,

which is exactly the same suggested sha value as on failing Windows tests.

[aignas]

@rickeylev, feel free to merge if you agree with the warning refactor.