Improve parser error recovery for misplaced `ref` modifier of a struct declaration

[DoctorKrolic]

Case 1:

Snippet:

ref public struct MyStruct;

Expected:
ref is in the modifiers list for MyStruct, error about its misplacement

Actual:
ref is a part of RefTypeSyntax of IncompleteMemberSyntax while StructDeclarationSyntax starts from a public token. The error is 'Type expected' on public token

Case 2:

Snippet:

partial ref struct MyStruct;

Expected:
partial is in the modifiers list for MyStruct, error about its misplacement

Actual:
partial is its own IncompleteMemberSyntax. The error is on ref keyword saying about its misplacement instead