Ensure eLayerSkipScreenshot doesn't hide layers on external displays

eLayerSkipScreenshot is enforced through separate paths for screen
recording and screen capture.  Prior to this change, for screen
recording, LayerSnapshotBuilder hid mirrored LayerSnapshots when
eLayerSkipScreenshot was set. For screen capture, CompositionEngine
enforced the flag via LayerFilter::toInternalDisplay, filtering out any
layers with eLayerSkipScreenshot when not presenting to an internal
display. The second mechanism caused an issue when using connected
displays. Connected displays aren't internal so eLayerSkipScreenshot
layers were hidden, despite the display not being used for screen
recording or capture.

To fix this issue, the CompositionEngine mechanism is updated to use a
new field, LayerFilter::skipScreenshot. For Outputs,
LayerFilter::skipScreenshot is true only for ScreenCaptureOutputs. For
Layers, LayerFilter::skipScreenshot is true if the layer sets
eLayerSkipScreenshot. This change fixes the issue where
eLayerSkipScreenshot layers are hidden on connected displays but breaks
screen recording scenarios where a layer is being recorded instead of an
entire display because CompositionEngine will no longer filter out
eLayerSkipScreenshot on virtual displays. To fix screen recording, the
LayerSnapshotBuilder mechanism is extended to enforce the flag whenever
layer mirroring is used (as opposed to only enforcing it for display
mirroring).

Bug: 418143858
Flag: com.android.input.flags.connected_displays_cursor
Test: composition engine tests, SF frontend unit tests, manual verification
Change-Id: I311b38682b03896648a21d2291ccc4cc7a239bbe