feat(plugins): let a code action create, rename and delete files (#1778)

A new optional file-actions export (worlds plugin-file-actions / file-actions-provider, API 1.3) lists quick fixes whose operations (create with text, rename, delete) and text edits are applied as one workspace edit, so a failure changes nothing and one undo reverses it; paths stay inside the project root, and `open` shows a file once the action is applied. Like providers' code actions, an action can carry only `data` and get its operations from `resolve` when picked.

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

wit/plugin.wit

@@ -86,6 +86,12 @@ world plugin-commit-checks {
     export commit-checker;
 }
 
+/// A plugin with file-changing code actions (`file-actions`, next to `[[contributes.providers]]`).
+world plugin-file-actions {
+    include plugin;
+    export file-actions;
+}
+
 /// Only the `syntax-provider` export: guests generate it next to `plugin`
 /// (the component tools merge both into one component).
 world syntax {
@@ -129,3 +135,8 @@ world details {
 world commit-checks {
     export commit-checker;
 }
+
+/// Only the `file-actions` export, generated next to `plugin` like `syntax`.
+world file-actions-provider {
+    export file-actions;
+}