feat(lsp): Implement an add graindoc code action

[spotandjake]

This pr implements an add graindoc code action that lets you add a graindoc template to let expressions and modules.

by default for a value or module we add:

/**
 *
 *
 * @example
 *
 * @since
 */

and for a function we add:

/**
 *
 *
 *
 * @param a:
 * @param b:
 * @returns 
 * @example
 *
 * @since
 */
provide let x = (a, b) => a + 1

This pr isn't quite ready to merge as it still needs tests but I wanted to get some feedback on this before writing those.

Closes: #2301

[spotandjake]

Tests have been added

Just some notes in response to the community call:

• The tab jumps thing that was mentioned over the community meeting isn't something we can do in a code action; this is something we can implement when we get autocomplete and have autocompleted doc blocks.
• I don't think we should have placeholder descriptions, as I think they are more likely to get left there by the user.
• If we like the code action, I'll come back in the future and open a pr to add it in more places, such as type definitions and the parent module description, as they'll take more work.

[spotandjake]

I wasn't quite sure if this is worthy of a code commnt, but this number should be Int.max_int however it seems that yojson treats these internally as IEEE-754 and we are getting some rounding.