Add elm treesitter textobjects

[magopian]

Fixes #6083

This is a first (naive) attempt at adding treesitter text objects for the elm language.

To test this out, copy the textobjects.scm file to your runtime folder in runtime/queries/elm and restart helix.

To find where your runtime folder is, use hx --health | grep runtime.

It should now allow you to select

• the code of function with mif
• the function itself with its optional type annotation with maf
• a function parameter with mia or mac
• a line of block comment with mic or mac

And you can navigate with the same text objects, so

• previous or next function with [f or ]f
• previous or next parameter with [a or ]a
• previous or next comment with [c or ]c