Fix race condition between PromptIconViewBinder and BiometricSizeBinder

Sets BiometricPrompt view invisible until all resizing is complete. Adds
new MutableStateFlow updated on iconView onCompositionLoadedListener,
and combines this new flow with the BiometricSizeBinder viewModel.size
collect call, to force the resizing logic to wait for the iconAsset to
update first to account for it in the prompt size. Reworking of
ag/25666425 to avoid CTS failures the original CL caused

Flag: NONE
Fixes: 313605043
Bug: 317291041
Test: atest CtsBiometricsTestCases
Test: (manual) manually verified prompt appears only once and in the correct size, no resizing visible to the user
Change-Id: Ic3cbf1785737c19c5434030d45a73b2435328a71