Add semantic highighting for def endless and singleton method names

[wildmaples]

Motivation

More semantic highlighting for method names of: def endless and singleton

Implementation

Create a visit method for both these types of methods

Automated Tests

Added new expectation file for semantic highlighting tests for the two new cases

Manual Tests

Turn on VS Code's editor token and scope mode:

def baz = 10

def self.foo
  a = 2
  puts "a"
end

[vinistock]

Good to go, once the order of visits concern is addressed

[wildmaples]

Good to go, once the order of visits concern is addressed

Already done! I fixed up the change