Add knip linter (#36442)

This adds [knip](https://github.com/webpro-nl/knip), a tool to find
unused files, dependencies and exports in JS. Fixed all discovered
issues.

1. knip apparently has some issue resolving imports from `d.ts` to `.ts`
so I worked around it by moving the two affected types to where they are
used.
2. I don't know why `modules/fomantic/dropdown.ts` had a new typescript
error, but I fixed it.
3. Use named export for `EsbuildPlugin`, I think this was added
recently.

Makefile

@@ -317,11 +317,13 @@ lint-backend-fix: lint-go-fix lint-go-gitea-vet lint-editorconfig ## lint backen
 lint-js: node_modules ## lint js files
 	$(NODE_VARS) pnpm exec eslint --color --max-warnings=0 $(ESLINT_FILES)
 	$(NODE_VARS) pnpm exec vue-tsc
+	$(NODE_VARS) pnpm exec knip --no-progress --cache
 
 .PHONY: lint-js-fix
 lint-js-fix: node_modules ## lint js files and fix issues
 	$(NODE_VARS) pnpm exec eslint --color --max-warnings=0 $(ESLINT_FILES) --fix
 	$(NODE_VARS) pnpm exec vue-tsc
+	$(NODE_VARS) pnpm exec knip --no-progress --cache --fix
 
 .PHONY: lint-css
 lint-css: node_modules ## lint css files