[ty] List available members for a given type (#18251)

This PR adds initial support for listing all attributes of
an object. It is exposed through a new `all_members`
routine in `ty_extensions`, which is in turn used to test
the functionality.

The purpose of listing all members is for code
completion. That is, given a `object.<CURSOR>`, we
would like to list all available attributes on
`object`.

crates/ty_python_semantic/resources/mdtest/binary/in.md

@@ -0,0 +1,53 @@
+# Static binary operations using `in`
+
+## Basic functionality
+
+This demonstrates type inference support for `<str-literal> in <tuple>`:
+
+```py
+from ty_extensions import static_assert
+
+static_assert("foo" in ("quux", "foo", "baz"))
+static_assert("foo" not in ("quux", "bar", "baz"))
+```
+
+## With variables
+
+```py
+from ty_extensions import static_assert
+
+x = ("quux", "foo", "baz")
+static_assert("foo" in x)
+
+x = ("quux", "bar", "baz")
+static_assert("foo" not in x)
+```
+
+## Statically unknown results in a type error
+
+```py
+from ty_extensions import static_assert
+
+def _(a: str, b: str):
+    static_assert("foo" in (a, b))  # error: [static-assert-error]
+```
+
+## Values being unknown doesn't mean the result is unknown
+
+For example, when the types are completely disjoint:
+
+```py
+from ty_extensions import static_assert
+
+def _(a: int, b: int):
+    static_assert("foo" not in (a, b))
+```
+
+## Failure cases
+
+```py
+from ty_extensions import static_assert
+
+# We don't support byte strings.
+static_assert(b"foo" not in (b"quux", b"foo", b"baz"))  # error: [static-assert-error]
+```