vim: Add g M motion to go to the middle of a line

[x4132]

Adds the "g M" vim motion to go to the middle of the line.

Release notes:

• vim: Added support for gM to go to the middle of a line

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[x4132]

@cla-bot check

[cla-bot]

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[ConradIrwin]

Thanks for this! Could you also please add a test.

You should be able to copy one of the existing ones that use NeovimBackedTestContext. When you run it with cargo test -p vim --features neovim -- my_test_name it'll generate a JSON file that you need to commit too.

[x4132]

For some reason the deletion behavior doesn't seem to be the same as neovim, even though cursor movement is the same.

# initial state:
ˇthe quick brown fox
jumped over the lazy dog
# keystrokes:
d v g M
# currently expected:
ˇbrown fox
jumped over the lazy dog
# neovim (NORMAL):
ˇbrown fox
jumped over the lazy dog
# zed (NORMAL):
ˇ brown fox
jumped over the lazy dog

[zed-industries-bot]

	Warnings
⚠️	This PR is missing release notes. Please add a "Release Notes" section that describes the change: Release Notes: - Added/Fixed/Improved ... If your change is not user-facing, you can use "N/A" for the entry: Release Notes: - N/A

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[ConradIrwin]

@x4132 Although it's not clear in the vim docs, gM is an exclusive motion. Updating that match statement fixed the tests you added :D.