feat(plugins): file marketplace plugins under categories

`plugin.toml` takes `categories` (up to 3 of languages, themes, icon-themes,
linters, vcs, ai, frameworks, tools, other). A plugin that declares none is
filed under what its contributions imply (themes, icon themes, languages),
else under other; categories an IDE doesn't know are ignored, and `check`
warns about them. Index entries carry the categories, and Settings › Plugins
› Available filters by them and shows them in a plugin's details. The
official plugins declare theirs.

plugins/official/string-tools/dist/plugin.wasm.sources

@@ -1 +1 @@
-a88c39d5782369329efa55b12330daa906e5c8d91252bd57c7343648840bac79
+09cc92e8e731f8f59f3857a71f9a30cc3d9e04a1c32092920f573b0f26592855