Fix Talkback Shortcut Vulnerability

The way the talkback component was selected was vulnerable. Now the
system verifies that the talkback component is provided by the system.

Bug: 339609745
Change-Id: Iabadb129807b0ac02aa2e9ac1580ac0f212930ef
Test: manual - tested that the talkback service is still available
Flag: No Flags: Security High/Critical Severity CVEs