These were just added to avoid churn when changing the default
of 'display'. To simplify message handling logic, we might want
to remove support for printing messages in default_grid later on.
This would allow things like printing error messages safely in the
middle of redraw, or a future graduation of the 'multigrid' feature.

This reverts commit 7ac5359143ef25c4c8c0c427d5533f8d5824ed17.
This fix can cause more problems than it solves.

Problem:    When there is a partially matching map and modifyOtherKeys is
            active a full map may not work.
Solution:   Only simplify modifiers when there is no matching mapping.
            (closes vim/vim#8792)
https://github.com/vim/vim/commit/196c3850dbe95247f7aa1b0000a5cae625a99ef2

Omit test as it sends terminal codes. Use a Lua test instead.

Problem:    CTRL-R CTRL-R doesn't work with modifyOtherKeys.
Solution:   Allow key codes when fetching argument for CTRL-R. (closes vim/vim#5266)
            Also fix CTRL-G in Insert mode.
https://github.com/vim/vim/commit/38571a04b4eb2853f46df8884750bcb9a8115db8

Omit test as it sends terminal codes. Use a Lua test instead.

Problem:    Mapping with partly modifyOtherKeys code does not work.
Solution:   If there is no mapping with a separate modifier include the
            modifier in the key and then try mapping again. (closes vim/vim#6200)
https://github.com/vim/vim/commit/975a880a1389e8ce6dea8d66a7c109140b2f94ec

Cherry-pick applicable part of put_string_in_typebuf().
Revert related changes from 10a5825.
Use KEYLEN_PART_KEY for incomplete modifier sequence.
Omit test as it sends terminal codes. Use a Lua test instead.

Problem:    Dropping modifier when putting a character back in typeahead.
Solution:   Add modifier to ins_char_typebuf(). (closes vim/vim#6158)
https://github.com/vim/vim/commit/b42c0d54279b1fdb79652db0c84171e213458809

Vim's test doesn't seem to work properly as the hit-enter prompt seems
to be delayed. Add a Lua screen test.

Problem:    With modifyOtherKeys CTRL-^ doesn't work.
Solution:   Handle the exception.
https://github.com/vim/vim/commit/828ffd596394f714270a01a55fc3f949a8bd9b35