Issue #3629679: Make the Accordion, Tabs, Icon and Social Icons blocks work

Closes #3629679

Accordion, Tabs, Icon and Social Icons are stable blocks in Gutenberg 24, but didn't work on Drupal.

Changes

• Interactivity API: fit-text-view stays in the preserved libraries of gutenberg-dependencies.php, next to interactivity. (#3628775 already pointed gutenberg/interactivity to index.js on 4.0.x, so the view scripts of accordion, tabs, file and playlist run.)
• Block context: GutenbergFilter gives inner blocks the context of their ancestors (providesContext in block.json, with defaults). It's in $block['context'] and in a new block_context template variable, and hook_gutenberg_block_context_alter() is the counterpart of render_block_context.
• Accordion: ports the upstream render onto the saved markup, so the templates keep what save() wrote (e.g. role="group"). Drupal doesn't process directives on the server, so the preprocess also writes their initial state (aria-expanded, hidden="until-found" on closed panels).
• Tabs:
  • Uses the current blocks (core/tab-list, core/tab-panels, core/tab-panel) in gutenberg.blocks.yml and the always-registered child blocks.
  • Ports their render, with the tab IDs passed through block context.
  • copy-block-assets.js removes the vendor directories of blocks that block-library no longer ships: the old Tabs blocks and the Form blocks, which are also gone from the allowed blocks.
• Icon:
  • gutenberg.icon_registry serves the public icons of @wordpress/icons, labelled "Gutenberg" and copied by scripts/copy-icons.js during build:vendor, plus the collections that themes and modules declare with icons: in their *.gutenberg.yml.
  • /editor/icon-collections and /editor/icons back the mocked /wp/v2/icon* paths.
  • A preprocess renders the SVG with the color, border, padding and width of the block.
  • Sizes: themes can offer sizes with dimensions.dimensionSizes, for one block in __experimentalFeatures.blocks.core/icon. PresetCssGenerator now defines the --wp--preset--dimension--* variables, and the presets of blocks on the block's .wp-block-* class. Editors can still enter a custom width; upstream has no setting to prevent it. Without a width, an icon is 24px, the default of the theme.json of WordPress (:root :where(.wp-block-icon svg) in css/blocks-view.css and the editor styles); block-library alone makes it as wide as the content.
• Social Icons: links follow "Open links in new tab", "Show text" and the icon colors of their Social Icons block.
• Math: the block saved an empty <math>. It loads @wordpress/latex-to-mathml with import(), which wraps the window.wp.latexToMathml global in a namespace whose default is the global itself, so the editor threw e.default is not a function. latex-to-mathml is now in DEFAULT_EXPORT_PACKAGES of webpack.vendor.config.js, like api-fetch. This also fixes the inline math format. Math blocks saved before get their MathML back when they are edited and saved again.
• Skipped serialization: wp_should_skip_block_supports_serialization() is ported from upstream, so Button, Image, Table, Separator and Icon no longer get their skipped supports on the wrapper.
• Base theme:
  • Styles Accordion (the Details look) and Tabs in the design system.
  • Registers its Lucide icons as the "Gutenberg Base" icon collection, and offers four icon sizes from its spacing scale.
  • Turns on the dimension controls that appearanceTools of its theme.json implies; without them the Icon block had no Width control.
  • Keeps social icons as tall as the icon (the link was inline-flex in a line box).
  • Centers the accordion chevron on the title.

Content saved with the experimental Tabs blocks (Gutenberg 23 and earlier) has no upstream migration and shows as unsupported blocks.

Testing

• New Playwright specs: accordion-tabs, icon, math and social-links (the last also covers Button serialization).
• Manually: allow the blocks on a content type, then add them with the base theme as default theme.