feat(cmdline): Add format for := lua expr

[mikesmithgh]

Hey @folke there was a new commit on nightly neovim/neovim@a92b389 with a shorthand syntax := for :lua cmdline. This feature is to match the pattern and format with the lua icon.

My autoformatter added the whitespace, let me know if you want me to remove it.

The := {expr} syntax can be used to evaluate a lua expression, as
a shorter form of :lua ={expr}. := and :[range]= without argument
are unchanged. However :=# and similar variants using |ex-flags|
are no longer supported.

[folke]

Thank you for this PR!

I've changed the implementation quite a bit so that multiple patterns are now allowed for a cmdline item.
Also added better support for :lua=

[mikesmithgh]

Thank you for this PR!

I've changed the implementation quite a bit so that multiple patterns are now allowed for a cmdline item. Also added better support for :lua=

awesome, 👍 just gave it test and looks good to me.