Use location links for namespace and method definition response

[vinistock]

Motivation

I noticed that we were unable to go to definition for constants that were referenced inside their own declaration. E.g.:

class Foo
  Foo
end

At first, I thought something was wrong with constant resolution, but it was not the case. We were always returning the class' complete location back to the editor (including the body part). This makes the editor consider any attempts to go to definition of the same symbol as a references rather than a definition request.

In reality, we only want the reference request to be invoked if someone CMD clicks the Foo declaration, but not a constant reference like the one in line 1.

Implementation

The spec provides the location link type to handle situations like these.

Location links allow us to return two locations:

1. targetRange: this is the complete range including the body. This is used to show a preview of the location that you are about to jump to
2. selectionTargetRange: this is the specific location that you will jump to, which is supposed to be only the identifier of the symbol

By using location links and passing only the identifier locations for namespaces and methods, then the editor does the right thing and allows us to correctly jump to definition for constant references inside their own declarations.

1. The first commit makes the return type of resolve more specific to avoid any typing issues
2. The second commit starts indexing name locations only on the entries in which it is relevant to do so. Note that RBS does not provide us with the two locations, so I'm falling back to assigning the same location to both - which should be fine since you cannot write a constant reference inside RBS anyway (you can only write declarations)
3. Finally, we start using location links for class, module and method definition requests

Automated Tests

I adapted the existing tests, but because this specific scenario requires full interaction with the editor, I could not manage to get a test working properly.

Manual Tests

On main, when you cmd click a constant reference that exists inside its own declaration, the editor will show "no references found for Foo" (because we don't implement the references request yet).

On this branch, you will jump to the right declaration.

[Morriar]

You can also replace the selection_range in TypeHierarchySupertypes: https://github.com/Shopify/ruby-lsp/blob/main/lib/ruby_lsp/requests/type_hierarchy_supertypes.rb#L85

[vinistock]

@Morriar done! Good catch.