Return semantic tokens for local vars shadowed by parameters

[vinistock]

Motivation

There was an oversight from by part in #2482. There's still one scenario where we don't want to avoid returning local variable tokens for all assignment types: when the variable is being shadowed by a parameter.

For example

def foo(a)
  # This should be highlighted as a parameter, since it was first declared as one
  # inside this scope. And the developer should know that they are overriding a parameter
  a = 123
end

Implementation

Essentially, I brought back all of the methods removed in #2482, but now we only return tokens if the variable has been shadowed by a parameter.

Automated Tests

Added a fixture and expectation that captures all cases.