feat(plugins): share project HTTP endpoints with the HTTP client (#1991)

Adds the API 1.3 `endpoints-provider` export and `[[contributes.endpoints]]` (file globs, ^1.3, `project.read`). A plugin's routes join the Spring ones in Search Everywhere, `.http` URL completion and the declaration's Open in HTTP Client gutter action. The UI asks `plugin_endpoints` on demand; the host runs the plugin on a blocking thread, validates the whole list (bounds, project-relative locations, UTF-16 ranges) and caches it per project until a file matching the globs changes, then emits `EndpointsChanged`. A failed or invalid run keeps the last list; disabling, crashing or closing the project withdraws it, and late results can't restore it. Closes #1960.

Co-authored-by: arnaud-ritti <[email protected]>

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

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