LSP Code Action: Generate dynamic decoder

[GearsDatapacks]

Closes #2955
This PR implements a code action to generate a dynamic decoder for a custom type.

[GearsDatapacks]

Oh, do we want to add support for decoding tuples as well? If so, what would that decoder look like (I've only done basic decoding thus far)

[lpil]

Yes please! Something like this:

use hostname <- decode.field("hostname", decode.string)
use ip <- decode.field("ip", {
  use a <- decode.field(0, decode.int)
  use b <- decode.field(1, decode.int)
  use c <- decode.field(2, decode.int)
  use d <- decode.field(3, decode.int)
  decode.success(#(a, b, c, d))  
})
decode.success(Server(hostname:, ip:))

[GearsDatapacks]

Ah I see, you can use field with more than just strings. Thanks!

[lpil]

Super cool! Neat how little code it is too. Very clean! Thank you!

[lpil]

Could we remove these empty lines please 🙏

[lpil]

I'll do it 👍