Tests: Add PHPUnit tests for location rule classes

[priethor]

What

Part of #315.

Adds PHPUnit test coverage for all 23 location rule classes that determine when and where field groups appear in the WordPress admin.

Why

Location rules are critical for controlling field group visibility. They handle complex matching logic including:

• Post type, status, format, template, and taxonomy matching
• Page hierarchy (parent/type) and template matching
• User role and form context matching
• Widget, menu, options page, and block matching

How

Adding 139 tests across all location types:

• Base ACF_Location class methods (compare_to_rule, get_operators)
• Post-based locations (post_type, post, post_status, post_format, post_template, post_taxonomy, post_category)
• Page locations (page, page_parent, page_type, page_template delegation)
• User locations (user_role, user_form, current_user, current_user_role)
• Form/other locations (taxonomy, attachment, comment, nav_menu, nav_menu_item, widget, options_page, block)
• Location type registration and retrieval functions

Testing Instructions

Run the test suite:

./vendor/bin/phpunit --filter Test_Location_Rules

[github-actions]

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Props priethor.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 21.78%. Comparing base (402b2cc) to head (fbd2c5a).
⚠️ Report is 2 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #329      +/-   ##
============================================
+ Coverage     21.19%   21.78%   +0.59%     
  Complexity     4410     4410              
============================================
  Files           291      291              
  Lines         36940    36940              
============================================
+ Hits           7828     8047     +219     
+ Misses        29112    28893     -219     

Flag	Coverage Δ
e2e	28.87% <ø> (ø)
javascript	2.50% <ø> (ø)
phpunit	21.87% <ø> (+0.81%)	⬆️

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