Support PostBack.Handlers in CompositeControls #2668

Job	Run time
Build published projects without warnings (Release)	3m 36s
JS unit tests	1m 50s
Build all projects without errors	11m 56s
.NET unit tests (ubuntu-latest)	5m 0s
Build published projects without warnings (Debug)	4m 23s
.NET unit tests (windows-2022)	10m 8s
UI tests (chrome, ubuntu-latest, Production, Default)	18m 10s
.NET unit tests (macOS-latest)	6m 22s
UI tests (chrome, windows-2022, Development, Default)	22m 31s
UI tests (firefox, ubuntu-latest, Development, Default)	21m 9s
UI tests (firefox, ubuntu-latest, Production, Default)	21m 6s
UI tests (firefox, ubuntu-latest, Development, ExperimentalFeaturesTests)	21m 35s
UI tests (chrome, ubuntu-latest, Production, ExperimentalFeaturesTests)	15m 51s
	2h 43m 37s

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