Issue #3537359: Empty settings for nested patterns.

Problem

Field group patterns configured as nested patterns (e.g., heading patterns inside item_list patterns) were losing their individual settings during recursive rendering. Pattern-specific configurations like heading level (h1, h2, h3) and style variants (primary, secondary) were not preserved, causing all nested patterns to render with default values.

Root Cause

In PatternFormatter::preRenderGroup(), when processing nested field group patterns recursively, the pattern settings from format_settings['pattern_settings'][pattern_id] were not forwarded to the render element's #settings property.

Solution

• Forward pattern settings to #settings during recursive processing of nested field group patterns
• Ensure nested patterns retain their individual configuration values
• Settings are then properly processed by UiPatternsRender::processSettings() into template variables

Test Coverage

• Added heading and item_list test patterns with configurable settings
• Added functional tests verifying nested patterns preserve individual settings
• Tests cover single and multiple nested pattern scenarios

Changes

• PatternFormatter.php: Add settings forwarding for nested patterns
• New test patterns and templates in ui_patterns_render_test module
• NestedPatternOptionsTest.php: Comprehensive functional test coverage

Fixes #3537359