Update Talkback text for app header "menu".

So now this is updated to "App Name - Double Tap to 'Open menu'. 'Open
Menu' is the text supplied by the string resource.

Bug: 329208268
Test: Manual. Turn Talkback on, focus on App Header for Settings - says
"Settings - Double tap to open menu".
Flag: EXEMPT bugfix
Change-Id: Id92aecb06676d5a63aba379f65db1a6af422d65b

Change-Id: I55104d3ae2cc3ee7b463644b9c054c5dd2aed052