Problem: Various code not covered by tests.
Solution: Add a few more test. (Yegappan Lakshmanan, closesvim/vim#7995)
1f448d906b
Cherry-pick some test_edit.vim changes from patches 8.2.{1022,1432}.
Reorder test_undo.vim to match upstream.
Neovim already removed `evim` (or any similar flags). The 'insertmode'
option is a weird remnant, so get rid of it.
The 'insertmode' option is replaced with a script that closely emulates
the option. This script is documented at :help 'insertmode'
Test_edit_08() depends on special-case handling in has_compl_option()
and redrawing() which are in Vim but are not wanted in Nvim. Using a Lua
test instead of depending on workarounds in the core to make the VimL
test work.
