audio policy: refine strategy invalidation logic take two

This reverts commit ea04dff4 and adds a proper fix
for b/140545518 to commit 8bbd0e14.
Direct outputs should follow a different logic for client invalidation
than mixer outputs.

Bug: 140545518
Test: audio smoke tests while verifying no audioserver crash.
Change-Id: Ia59803f10a7eeb2f02803b9a07630c744a37bf02