Add tff_mappings tool to show found or missing tests.yml mappings

What does this MR do and why?

This MR adds a new script tooling/bin/tff_mappings to show mappings for test_file_finder defined in tests.yml.

Useful to compare results before and after tests.yml has changed. For example: !150981 (merged)

Contributes to #432986.

⚠ This script does not have any specs because it's not used in any automation.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Example outputs

Some example outputs

$ tooling/bin/tff_mappings -h
Usage: tooling/bin/tff_mappings [options] [<file> ...]
        --found                      Show found tff mappings.
        --missing                    Show missing tff mappings.
        --ignored                    Show ignored files.
        --all                        Show all states: found, missing, and ignored.
        --[no-]summary               Show summary of found and missing entries. Default: true
    -h, --help                       Show this help.

$ tooling/bin/tff_mappings
# total=71940 found=27678 missing=18650 ignored=25612

$ tooling/bin/tff_mappings --missing --no-summary config/initializers
config/initializers/00_active_record_disable_cross_database.rb
config/initializers/00_active_record_disable_joins.rb
config/initializers/00_rails_disable_joins.rb
config/initializers/01_secret_token.rb
config/initializers/0_as_concern.rb
config/initializers/0_eager_load_http_cookie.rb
[...]

$ tooling/bin/tff_mappings --all config/initializers | tail
config/initializers/validate_puma.rb FOUND
config/initializers/warden.rb MISSING
config/initializers/webauthn.rb MISSING
config/initializers/webhook_recursion_detection.rb MISSING
config/initializers/wikicloth_disable_lua_patch.rb MISSING
config/initializers/wikicloth_redos_patch.rb MISSING
config/initializers/wikicloth_ruby_3_patch.rb MISSING
config/initializers/workhorse_multipart.rb MISSING
config/initializers/zz_metrics.rb MISSING
# total=185 found=49 missing=136 ignored=0