libgui: Fix broken buffer locking tests

These tests were broken because they would request usages when locking
that were different than those provided at creation time.

The Surface::lock implementation was updated to also set usage
appropriately.

Bug: 419599106
Flag: EXEMPT broken tests and simple changes
Test: atest libgui_test
Change-Id: I525798a7684a1526fa3c051761525d92d9066241