Samsung's Korean keyboard has a bug where it always attempts to combine
characters based on its internal state, ignoring if and when the cursor
is moved programmatically. EG typing "ㄴㅇ" and then moving the cursor
back to the front of the text and typing "ㄴ" again would result in
"ㄴㅇㄴ", not "ㄴㄴㅇ".
Fully restarting the IMM works around this because it flushes the
keyboard's internal state and stops it from trying to incorrectly
combine characters. However this also has some negative performance
implications, so we only apply the workaround on Samsung devices set
to use Korean input.
This also effectively disables the feature on Samsung keyboards that
allowed users to re-open a composing region for previously typed
characters. See https://github.com/flutter/flutter/issues/29341#issuecomment-531283508.
Fixesflutter/flutter#29341.
Gary Qian
Dan Field
Justin McCandless
Jason Simmons
Michael Klimushyn