Fix --remote_download_regex matching all files unconditionally (#3301)

#### Summary

Fix a bug in `generate_index_build_bazel_dependencies.sh` where the
`--remote_download_regex` pattern matches all files unconditionally,
defeating the purpose of selective downloads during Index Build.

#### Problem

The current regex:
```
--remote_download_regex=${indexstores_regex}.*|.*\.(cfg|c|C|cc|...)$
```

The `.*|` at the boundary acts as an unbounded wildcard. Due to regex OR
semantics, it matches every file before the alternation is even
evaluated. This means all remote cache outputs are downloaded locally
during Index Build, regardless of file extension.

The intent was to download only indexstores (matched by
`${indexstores_regex}`) and files with indexing-relevant extensions
(`.swiftmodule`, `.swiftdoc`, `.swift`, headers, etc.). Instead, every
output, including `.o` files, intermediate artifacts, and linked
binaries, is downloaded.

#### Fix

Remove the erroneous `.*|` so the regex correctly constrains downloads
to indexstores and listed extensions only:

```
--remote_download_regex=${indexstores_regex}.*\.(cfg|c|C|cc|...)$
```

#### Impact

In a large-scale monorepo, this bug caused Index Build's local storage
to grow from an expected few GB to over 1TB, as all remote cache outputs
were downloaded unconditionally. With the fix, only indexing-relevant
files are downloaded.

#### Related

- #3078

Signed-off-by: Ryo Aoyama <r.fe51028.r@gmail.com>

Author: ra1028

xcodeproj/internal/bazel_integration_files/generate_index_build_bazel_dependencies.sh

@@ -56,7 +56,7 @@ readonly build_pre_config_flags=(
   # This is brittle. If different file extensions are used for compilation
   # inputs, they will need to be added to this list. Ideally we can stop doing
   # this once Bazel adds support for a Remote Output Service.
-  "--remote_download_regex=${indexstores_regex}.*|.*\.(cfg|c|C|cc|cl|cpp|cu|cxx|c++|def|h|H|hh|hpp|hxx|h++|hmap|ilc|inc|inl|ipp|tcc|tlh|tli|tpp|m|modulemap|mm|pch|swift|swiftdoc|swiftmodule|swiftsourceinfo|yaml)$"
+  "--remote_download_regex=${indexstores_regex}.*\.(cfg|c|C|cc|cl|cpp|cu|cxx|c++|def|h|H|hh|hpp|hxx|h++|hmap|ilc|inc|inl|ipp|tcc|tlh|tli|tpp|m|modulemap|mm|pch|swift|swiftdoc|swiftmodule|swiftsourceinfo|yaml)$"
 )
 
 source "$BAZEL_INTEGRATION_DIR/bazel_build.sh"