Refactoring Text Editor (in progress)

Insert/Delete/Backspace
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Change-Id: I38727ddb86bf20cdd6c64363c33ffda03ab3c2c7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/431179
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Julia Lavrova <jlavrova@google.com>
24 files changed