Feature: Add support for asdf's .tool-versions file

[yamadashy]

Describe the feature

Add support for reading PHP version from asdf's .tool-versions file in setup-php action. Currently, the action supports .php-version file, and adding support for .tool-versions would help users who use asdf for version management.

Similar to the current support:

- uses: shivammathur/setup-php@v2
  with:
    php-version-file: .tool-versions  # New proposal, similar to .php-version support

Please check the latest release

• I have checked releases, and the feature is missing in the latest patch version of v2.

Underlying issue

Projects using asdf for PHP version management currently need to maintain both .tool-versions for local development and either specify the version directly in workflows or maintain a separate .php-version file. Supporting .tool-versions would allow these projects to use a single source of truth for PHP versions across all environments.

The action already supports reading from .php-version, so extending this to support .tool-versions would be a natural evolution and help users who prefer asdf for version management.

Describe alternatives

Current alternatives:

1. Manually specify PHP version in workflow (requires manual sync with .tool-versions)
2. Maintain a separate .php-version file (requires maintaining two version files)
3. Use a script to generate .php-version from .tool-versions (adds complexity to workflow)

Additional context

Example .tool-versions file content:

php 8.3.13

Similar functionality exists in other GitHub Actions:

• actions/setup-node supports .tool-versions

- uses: actions/setup-node@v4
  with:
    node-version-file: .tool-versions

Are you willing to submit a PR?

Yes