Create a new icon cache mechanism for memory improvement

- Avoid loading all app icons at once to decrease memory usage.
- Implement AppIconCacheManager with LruCache to optimize cache usage.
- Create related APIs to access the icon cache conveniently.
- Enable the new cache mechanism for the Settings process.

Bug: 187118427
Bug: 209898662
Test: robotests & check memory trace of apps pages.
Change-Id: I3843d7ed00812b6923e3c6dc175f98d507f81b7b