Release 12.1.0 into trunk

[AliSoftware]

Releasing new version 12.1.0.

What's Next

PR Author: Be sure to create and publish a GitHub Release pointing to trunk once this PR gets merged,
copy/pasting the following text as the GitHub Release's description:

### New Features

- `ios_generate_strings_file_from_code` now accepts an `output_encoding:` optional parameter. [#591]
  This is typically useful if you prefer your generated files to be UTF-8 rather than the default UTF-16 that `genstrings` is using.

### Internal Changes

- Added the handling of remote to `GitHelper::point_to_same_commit?` [#590]