Smaller reactor handle locks (flutter/engine#56768)
This reduces the amount of work that is happening inside the read/write
mutex for tracking handles in the Reactor.
1) Now gl cleanup calls happen outside of the write lock
1) Now setting gl debug texts are out of the write lock
1) Now creating objects with CreateHandle are out of the write lock
Jonah was seeing considerable time in the rwmutex, this should alleviate
some of that.
issue: https://github.com/flutter/flutter/issues/159177
tests: no functional change, just performance
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