Conversion of AbstractSource.java to AbstractSource.kt in AOSP QuickSearchBox App

Used automated tool to convert AbstractSource.java to Kotlin code, fixing all errors and warnings arising from the conversion. Also configured Android.bp to build target QuickSearchBox with the new .kt files and added an exclude_srcs property for now unused java files. Built converted files against the latest version of Kotlin (-language-version 1.7)

Bug: 239665416

Test:  manual testing with bramble device, unit tests ran with atest QuickSearchBoxTests with result:
Summary (Test executed with 1 devices.)
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arm64-v8a QuickSearchBoxTests: Passed: 50, Failed: 0, Ignored: 0, Assumption Failed: 0,

All tests passed!

Change-Id: I16b521d2bc83be24ad9f22fae3c4cdfad65562c8