Update git submodules

* Update frameworks/support from branch 'androidx-main'
  to bcffc573c4324fc9699c2552d68daf2e6c1c77e5
  - Merge "Fix serialization signature checking." into androidx-main
  - Fix serialization signature checking.
    
    - Update all projects to use latest kotlin serialization plugin
    - Update the checksum in the metadata file
    
    Test: ./gradlew bOS --dry-run
    Change-Id: I7406dd77df83b3f9bdbd2e1166c55ad0e0089d17
    

* Update prebuilts/androidx/external from branch 'androidx-main'
  to 51341cc5932ed92f79708ea06dab6754842785a8
  - Merge "Add org.jetbrains.kotlin.plugin.serialization.gradle.plugin-1.6.10" into androidx-main
  - Add org.jetbrains.kotlin.plugin.serialization.gradle.plugin-1.6.10
    
    Test: Usage in androidx
    Change-Id: I7d55b378ffa95c68cf0a3c8acc936f7e68db0a5c