android_hardware_smoke_test: Improve reliability (#191374)

Issue https://github.com/flutter/flutter/issues/191348 shows that the
detection and retry behavior introduced in PR
https://github.com/flutter/flutter/pull/190110 did not solve the issue.

Previously, engine cache cleanup was placed solely in `@AfterClass
tearDownClass()`. When a test run failed mid-suite on attempt 1, JUnit
aborted before `@AfterClass` could run. When attempt 2 launched,
`MainActivity` retrieved the corrupted engine from cache, guaranteeing
that subsequent attempts failed with blank screenshots, which matches
what we see in the run history.

To fix this, we move cache cleanup to `MainActivity.evictEngineCache()`.
`FlutterActivityTest.kt` invokes this cleanup during class teardown and
whenever an `EglInitializationException` or `BlankScreenshotException`
occurs, ensuring any retry starts with a clean engine instance.

We also reduce the retry cap in `run_android_hardware_smoke_tests.dart`
from 3 attempts to 2 to avoid 30-minute LUCI timeouts on broken
emulators, which we saw some of in tryjobs.

I think this should be an infrastructure failure. So if an unrecoverable
EGL collapse occurs across both attempts, the runner logs an
infrastructure failure and exits with code 2 (`INFRA_FAILURE`)

We also saw some logs which suggest HWUI repeatedly attempted 10-bit
color format negotiation (`101010-2`), which fails on SwiftShader CPU
drivers. This could contribute to an increased rate of EGL errors, so
`MainActivity.onCreate()` now explicitly locks the window pixel format
to `PixelFormat.RGBA_8888`.

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