feat: autofix unknown variable: a and file not found (searched at a.typ) by code action

[Myriad-Dreamin]

Example

from:

// unknown variable: first-item
#todo-list(first-item, second-item)

to

#let ${1:first-item} = ${2:none}

#todo-list(first-item, second-item)

Example

from:

// file not found (searched at a.typ)
#include "a.typ"

to

// a.typ
$0