Add hover actions LSP extension documentation.

docs/dev/lsp-extensions.md

@@ -467,3 +467,41 @@ interface InlayHint {
     label: string,
 }
 ```
+
+## Hover Actions
+
+**Client Capability:** `{ "hoverActions": boolean }`
+
+If this capability is set, `Hover` request returned from the server might contain an additional field, `actions`:
+
+```typescript
+interface Hover {
+    ...
+    actions?: CommandLinkGroup[];
+}
+
+interface CommandLink extends Command {
+    /**
+     * A tooltip for the command, when represented in the UI.
+     */
+    tooltip?: string;
+}
+
+interface CommandLinkGroup {
+    title?: string;
+    commands: CommandLink[];
+}
+```
+
+Such actions on the client side are appended to a hover bottom as command links:
+```
+  +-----------------------------+
+  | Hover content               |
+  |                             |
+  +-----------------------------+
+  | _Action1_ | _Action2_       |  <- first group, no TITLE
+  +-----------------------------+
+  | TITLE _Action1_ | _Action2_ |  <- second group
+  +-----------------------------+
+  ...
+```

editors/code/src/client.ts

@@ -66,7 +66,7 @@ export function createClient(serverPath: string, cwd: string): lc.LanguageClient
                             // Workaround to support command links (trusted vscode.MarkdownString) in hovers
                             // https://github.com/microsoft/vscode/issues/33577
                             hover.contents = hover.contents.map(toTrusted);
-                            
+
                             const actions = (<any>result).actions;
                             if (actions) {
                                 hover.contents.push(renderHoverActions(actions));