Makes local record field completion respects the fields sharing one single type signature

[konn]

Currently, HLS generates wrong completion snippets for a record with some fields sharing the same type signature.
For example, consider the following:

data Foo = Foo { arg1, arg2 :: Int, arg3 :: Int, arg4 :: Bool }

Above, arg1, arg2 shares the same Int signature and this is a completely legitimate definition.
If this is defined in a local module, the current HLS generates the following record snippet for Foo, which lacks arg2:

Foo { arg1 = _arg1, arg3 = _arg3, arg4 = _arg4 }

The base cause of this seems as follows.
HLS handles record snippets for datatypes in a local module via parsed modules (findRecordCompl logic), especially from the RecCon constructor.
In RecCon, field information is stored as a list of ConDeclFields, which stores field label information in cd_fld_names field.
This cd_fld_names is a list of LFieldOccs, and it seems that this nested structure reflects the signature-sharing relation.
The current implementation in HLS, however, picks only the first element of cd_fld_names, resulting in the incomplete completion snippet.

This PR aims at fixing this issue by just returning lists as-is.

[konn]

Oops, I somehow miss-clicked "remove request" link. I've just re-sent review request again.

[Ailrun]

LGTM