Feature/add gleam

[locnide]

This pull requests adds textobjects for gleam.

I mainly took inspiration from the rust textobject.scm.

Feel free to review, it is the first treesitter query file I wrote.

PR #715 is similar but seem abandonned.

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Some thing that I still have to implement before merge:

• trailing comma for parameter.outer. Currently trailing comma are ignored.
• add @assign.inner but I’m not sure what it should select, see What is assignment inner ? #852
• migrate my install to treesitter-nvim main… current CI issues mighnt be due to an obsolete parser I used for testing
• rebase and squash

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Some tags are not implemented in this PR:

• @attribute couldn’t find examples in languages I know. Are there supposed to be type/class attributes ?
• @comment.inner I would have to use directives
• @frame, @loop and @regex not relevant
• @scopename I do not know what it is

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P.S. : I had trouble making make docs work #854