Create processDisplayChangesLocked

This simply extracts the code in handleTransactionLocked for the
eDisplayTransactionNeeded case into its own function.

There were no changes other than a quick clang-format of the extracted function.

Bug: 38464421
Test: Builds
Change-Id: Id84f5b990fb6818db1f8b0c37ac02bf3caa26002
Merged-In: Id84f5b990fb6818db1f8b0c37ac02bf3caa26002
(cherry picked from commit 347200f0)