Migrate performance snippets

[pengzhi-cb]

This PR aims to add following hard-coded snippets from DAC to repo:
(3 snippets) Analysis optimization
(2 snippets) Best practices

Summary:

• Consolidated 2 methods that shared exact code into one.
• Added ellipses to indicate that surrounding or existing code has been omitted for brevity.
• Enabled build config in gradle.

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• compose/snippets/src/main/java/com/example/compose/snippets/performance/AnalysisOptimization.kt:23, tag android_performance_appstartup_strict_mode
• compose/snippets/src/main/java/com/example/compose/snippets/performance/PerformanceSnippets.kt:312, tag android_compose_performance_conditional_composition
• compose/snippets/src/main/java/com/example/compose/snippets/performance/PerformanceSnippets.kt:320, tag android_compose_performance_conditional_composition_effect

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[kkuan2011]

Thanks Peng, could you rename the title of the PR to something like Migrate performance snippets? Also feel free to remove any comments in the PR description if it refers to intermediate states of the PR and is not reflected in the final code (e.g. mentions of System.gc() can be removed now). I've also added our Performance DRE, Ajesh, for review on the PR too.

[pengzhi-cb]

Thanks Peng, could you rename the title of the PR to something like Migrate performance snippets? Also feel free to remove any comments in the PR description if it refers to intermediate states of the PR and is not reflected in the final code (e.g. mentions of System.gc() can be removed now). I've also added our Performance DRE, Ajesh, for review on the PR too.

Got it, since the final diff wouldn't show those intermediary changes and it will be confusing to reviewer. Let me remove.