This PR add basic support to indents.

Some cases that have not been implemented:

Variant

type user = 
 | Id
 | Name

How to set the node/rule where indentation ends?

Labeled Variant Payloads (Inline Record)

| is the cursor

type user =
 | Id
 | Name({|})

Press enter:

type user =
 | Id
 | Name({
 |
 })

Here the indentation not work because Name({}) is a ERROR. record_type rule require a field

ERROR [0, 0] - [2, 12]
 type_identifier [0, 5] - [0, 9]
 variant_declaration [1, 4] - [1, 6]
 variant_identifier [1, 4] - [1, 6]
 variant_identifier [2, 4] - [2, 8]

Could record_type be an optional rule to not generate an ERROR node in the parser?