swift234

[Type checker] Correctly resolve locators for ".foo" to static/class functions.

When resolving a particular locator for a ".foo" expression that
references a static/class function, make sure we pass through the
proper locator. Otherwise, when that ".foo" is somehow generic, we
won't be able to find the opened type and, therefore, will crash when
trying to form the substitution.

While I'm here, simplify the "default arguments owner" computation
logic to simply retrieve the callee declaration, which is useful for
more than just default arguments.