[clangd] Update theme when color theme changes in vscode extension.

[jvikstrom]

Summary

Add event listener that listens to configuration changes and reloads the theme when it changes.

[hokein]

the change looks good, but I'd wait until D66219 is finished.

[jvikstrom]

Updated to new master.

[hokein]

please update the description of the patch.

clang-tools-extra/clangd/clients/clangd-vscode/src/semantic-highlighting.ts

97

does conf.affectsConfiguration('workbench.colorTheme') work?

[jvikstrom]

Use conf.affectsConfiguration('workbench.colorTheme') instead of keeping track of the old color theme manually.

clang-tools-extra/clangd/clients/clangd-vscode/src/semantic-highlighting.ts

initialize(capabilities: vscodelc.ServerCapabilities,
     if (!serverCapabilities.semanticHighlighting)
       return;
     this.scopeLookupTable = serverCapabilities.semanticHighlighting.scopes;
     // Important that highlighter is created before the theme is loading as
     // otherwise it could try to update the themeRuleMatcher without the
     // highlighter being created.
     this.highlighter = new Highlighter(this.scopeLookupTable);
     this.subscriptions.push(vscode.Disposable.from(this.highlighter));
+    // Adds a listener to reload the theme when it changes.
+    this.subscriptions.push(
+        vscode.workspace.onDidChangeConfiguration((conf) => {
+          if (!conf.affectsConfiguration('workbench.colorTheme'))
+            return;
+          this.loadCurrentTheme();
+        }));
     this.loadCurrentTheme();
     // Event handling for handling with TextDocuments/Editors lifetimes.
     this.subscriptions.push(vscode.window.onDidChangeVisibleTextEditors(
         (editors: vscode.TextEditor[]) =>
             editors.forEach((e) => this.highlighter.applyHighlights(
                                 e.document.uri.toString()))));
     this.subscriptions.push(vscode.workspace.onDidCloseTextDocument(
         (doc) => this.highlighter.removeFileHighlightings(doc.uri.toString())));