WIP Update to Bootstrap 5

[malberts]

For #38
Fixes #66

Known TODOs:

• Modal does not trigger
• Popover does not trigger
• Test more with Chameleon 6 (WIP Update to Bootstrap 5.3 ProfessionalWiki/chameleon#476)
• Test with Medik

[malberts]

Closing — superseded by #74.

PR #74 is a clean 9-commit redo from master that:

• Replicates the BS5 migration class renames / data-bs-* attribute updates from this PR.
• Fixes the "Modal does not trigger" and "Popover does not trigger" TODOs from this PR's description. They turned out to be the same bug as the long-standing Tooltip, Popover and Modal stop working after a cache purge on MW 1.43.3 #68 (open since 2025-08-08) — ParserOutput::setExtensionData no longer survives the parse → OutputPageParserOutput hook lifecycle under MediaWiki 1.43+. Migrate to Bootstrap 5.3 and resolve modal/popover/tooltip lifecycle bug #74 closes Tooltip, Popover and Modal stop working after a cache purge on MW 1.43.3 #68 by emitting the modal markup inline instead of relying on the deferred-injection mechanism.
• Fixes a few smaller miscellaneous things this PR missed: the DOMContentLoading typo in modules/ext.bootstrapComponents.tooltip.js, Badge.php still emitting .badge-<color> (BS5 removed that family in favour of .text-bg-<color>), and a documentation pass across docs/components/*.md.
• Pins mediawiki/bootstrap at the released ^6.0 rather than the 6.x-dev constraint this PR used.

Verified on a 4-stack visual-regression harness (Chameleon BS4/BS5 × Medik BS4/BS5 on MW 1.43.8) including a comprehensive ~75-attribute matrix, and BC's PHPUnit suite (96 tests) passes.