[ty] Add more autofixes (#28029)
## Summary
Add a new `SemanticMode::definitely_has_builtin_binding()` that allows
us to cheaply and easily query whether a builtin name such as `list` or
`int` has been shadowed by a variable in an enclosing scope when viewed
from a given node in the AST. Once this method is in place, it becomes
much more trivial to add autofixes to various diagnostics, which this PR
therefore does.
The new method does not attempt to fully model Python's name-lookup
semantics. It doesn't need to -- it's okay to be conservative when
offering autofixes. The method therefore errs on the side of caution and
only returns `true` if it can be certain that the name passed in was
definitely not shadowed in an enclosing scope.
The new method is similar to the `SemanticModel::has_builtin_binding()`
method that Ruff has had for a long time.
The new `SemanticModel` method is pulled out of
https://github.com/astral-sh/ruff/pull/27634, where I'm using it for
several more diagnostic autofixes that make it much easier to understand
how ty is trying to tell you to rewrite your code (in my opinion).
## Test Plan
mdtests and snapshots
