Eliminate redundant variable treesit-admin--builtin-language-sources

Eliminate redundant variable treesit-admin--builtin-language-sources

Nowadays, each mode populates treesit-language-source-alist when the
mode is required; we do not need to duplicate the information.

* admin/tree-sitter/treesit-admin.el
(treesit-admin--builtin-language-sources)
(treesit-admin-verify-major-mode-queries)
(treesit-admin--generate-compatibility-report): Eliminate variable
treesit-admin--builtin-language-sources.
(treesit-admin--generate-compatibility-report): bash-ts-mode is “clever”
and switches back to sh-mode if it thinks the current buffer does not
contain a Bash script (bug#78747).
(treesit-admin--builtin-modes): Add missing modes.
(treesit-admin--builtin-features): New variable, telling us which
features to require to populate treesit-language-source-alist.
(treesit-admin--populated-treesit-language-source-alist): New function,
to add everything we know to treesit-language-source-alist.
(treesit-admin--unversioned-treesit-language-source-alist): Return a
copy of treesit-language-source-alist with the version requirements
removed.
* test/infra/Dockerfile.emba: Make use of
treesit-admin--populated-treesit-language-source-alist (bug#78748).

(cherry picked from commit 6181e0cec5158c5b66bf861c32e49674b2a110e9)