composeBox: Limit maxHeight to 60% of parent.
composeBox: Limit maxHeight to 60% of parent.

Provide max height in percentage so that it works in split-screen
mode, and even when keyboard appears.

Fixes: #3977

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile