Exclude unnecessary window early in DisplayWindowsObserver

Previously, some windows are excluded from the final list of
accessibility windows in populateReportedWindowLocked().
This is done after we compute touchable region to decide which windows
are touchable and to be exposed.
Thus, there are some corner cases where an unwanted window joins in
touchable region computation and occludes an important window,
resulting in missing window info.

With this change, unnecessary windows are excluded when we compute
touchable regions.

This is a retry of abandoned CL [1] with a cleaner approach behind
the computeWindowChangesOnA11y flag.

[1] Iacff5b7e67a9e7e989671dc85ad884b0e9f2f2f0

Bug: 240885392
Bug: 254581919
Test: android.autofillservice.cts.servicebehavior.SettingsIntentTest
Test: android.autofillservice.cts.inline.InlineTooltipTest
Test: CtsAccessibilityServiceTestCases CtsAccessibilityTestCases AccessibilityWindowManagerWithAccessibilityWindowTest
Change-Id: Id4b24284db40feaa744c9a5598d0067566fa3963