[sources] Rename "Add folder" to "Add folder manually".

Per Seed Deck[^1] for the "Automatic Workspace Folders" feature, the
"Add folder" toolbar button in the Workspace tab of the Sources panel
should be renamed to "Add folder manually" to make it clear that this
is different from the automatic workspace folder(s).

[^1]: http://go/chrome-devtools:automatic-workspace-folders-ux

Bug: 404170628
Change-Id: Ia13267a7ae543c86d8ab059b26c5b746013c3c3c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6439039
Commit-Queue: Alex Rudenko <alexrudenko@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>

Author: bmeurer

front_end/panels/sources/sources-meta.ts

@@ -189,13 +189,15 @@ const UIStrings = {
    */
   createNewSnippet: 'Create new snippet',
   /**
-   *@description Title of an action in the sources tool to add folder to workspace
+   * @description Button in the Workspace tab of the Sources panel, used to
+   *              (manually) add a folder to the workspace.
    */
-  addFolderToWorkspace: 'Add folder to workspace',
+  addFolderManually: 'Add folder manually',
   /**
-   *@description Title of an action in the sources tool to add folder to workspace
+   * @description Title of an action in the Sources panel command menu to (manually)
+   *              add a folder to the workspace.
    */
-  addFolder: 'Add folder',
+  addFolderToWorkspace: 'Add folder to workspace',
   /**
    *@description Title of an action in the debugger tool to previous call frame
    */
@@ -1976,7 +1978,7 @@ Common.Revealer.registerRevealer({
 UI.Toolbar.registerToolbarItem({
   actionId: 'sources.add-folder-to-workspace',
   location: UI.Toolbar.ToolbarItemLocation.FILES_NAVIGATION_TOOLBAR,
-  label: i18nLazyString(UIStrings.addFolder),
+  label: i18nLazyString(UIStrings.addFolderManually),
   loadItem: undefined,
   order: undefined,
   separator: undefined,