Don't generate code lens for nested definitions

[thomasmarshall]

Motivation

When testing a test framework or plugin, it's common to have test methods inside test methods. This change ensures that the code lens is only generated for tests that will actually be run by the test runner, not for nested definitions.

Before	After

Implementation

It tracks the depth of nested method definition nodes and returns early if the depth is greater than one level.

Automated Tests

I've added a test that ensures the code lens is generated for the outer test method but not the inner one.

Manual Tests

1. Write a test with a another test method inside

   def test_foo
     def test_bar
     end
   end

2. Confirm that code lens appears for test_foo but not test_bar