gutenberg 4.0.0-beta2

New: gutenberg_base theme with globalStyles support

Introduced the gutenberg_base starter theme — a full Drupal theme purpose-built for Gutenberg:

• globalStyles YAML support: typography, colors, spacing, block-level styles map to generated CSS
• GlobalStylesGenerator class: converts theme YAML to body, element, and block CSS rulesets
• Layout gap CSS generation: :where(.is-layout-flex) { gap }, :where(.is-layout-flow) > * + * rules
• CSS custom properties: --wp--style--block-gap, --wp--style--global--content-size, etc.
• Full theme scaffold: navigation, breadcrumbs, forms, pager, dark mode, node templates
• Fix: Editor style injection refactor (Issue #3445654)
• Removed CSS pre-transform in gutenberg.js; global styles now injected server-side only
• Gated frontend-only CSS (gutenberg_page_attachments) behind non-admin route check
• Cleaned up editorSettings.styles handling to avoid double-injection
• Fix: alignfull editor overflow and gallery layout (Issue #3445654)
• Added editor-overrides.css to gutenberg_base theme — cancels structural.css viewport-width rules (which overflow the editor canvas) with width: auto; margin: 0 for .alignfull
• Fixed gallery block styling: structural.css stays in editorSettings.styles because block-library/style.css explicitly excludes modern gallery markup via :not(.has-nested-images)

Fix: Frontend layout CSS cascade

Corrected CSS source-order so global styles override block-library vendor defaults:

• LayoutProcessor: now runs on all named blocks; gutenberg_render_layout_support_flag() handles its own early-return, so default-layout blocks (columns, group, etc.) now receive is-layout-* classes on the frontend
• block-supports-shims: gutenberg_get_global_settings() now bridges globalStyles.spacing.blockGap → settings.spacing.blockGap, enabling per-block gap CSS generation for flex/grid layout blocks
• CSS load order: block-library/style.css and theme.css moved from gutenberg/blocks-view library (css-placeholder, loads after html_head) to explicit
  elements injected in html_head before the inline global-styles tags — mirrors WordPress's global-styles depending on wp-block-library
• editor-overrides.css: mirrors frontend flow/constrained layout gap rules with class specificity (0,1,0) to override reset.css's p { margin: revert } at (0,0,1), matching editor paragraph spacing to the frontend

Fix: PHP 8.4 deprecation warnings

Addressed implicit nullable parameter deprecations across 7 files: gutenberg.module, OEmbedProcessor, MediaController, MappingFieldsHelper, BlockParser, ReusableBlockDelete, MediaService.