Cleaner ScreenshotArg struct init, function parameter cleanup

Uses a more readable syntax for ScreenshotArgs struct initialization
and places more screenshot args in the struct, reducing the length
of the parameter list for screenshot functions.

Bug: b/377758217
Test: atest SurfaceFlinger_test
Test: atest CompositionTest
Test: atest RegionSamplingtest
Flag: EXEMPT, refactor
Change-Id: I0d3c09d4ccfbe877b2d95065031efa5d64701acd