Finish attach appliation before creating app context

Creating the app context involves getting app resources from the app's
apk. This operation could be blocked on an incremental fs and trigger the proc start timeout.

While fixing this, I noticed that apps could also run code and block in
AppComponentFactory#instantiateClassLoader, so moved the call to finishAttachApplication even earlier.

It's probably worth re-thinking the AnR timeouts around proc starts, because currently, if the app blocks in instantiateClassLoader for instance, neither AnR timeout nor proc start timeout will trigger.

For now, this fixes the test and keeps the behavior as close to the old behavior as possible.

Test: atest CtsPackageManagerStatsHostTestCases:com.android.cts.packagemanager.stats.host.IncrementalAppErrorStatsTests#testAppCrashOnIncremental
Bug: 261009296
Change-Id: Ic75a4e9d38a7c21d4a0b948d6fb26389723a80f6