[red-knot] Minor simplifications and improvements to constraint narrowing logic (#15270)

crates/red_knot_python_semantic/resources/mdtest/narrow/isinstance.md

@@ -174,3 +174,11 @@ def _(flag: bool):
     if isinstance(x, int, foo="bar"):
         reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 ```
+
+## `type[]` types are narrowed as well as class-literal types
+
+```py
+def _(x: object, y: type[int]):
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: int
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/issubclass.md

@@ -239,3 +239,11 @@ t = int if flag() else str
 if issubclass(t, int, foo="bar"):
     reveal_type(t)  # revealed: Literal[int, str]
 ```
+
+### `type[]` types are narrowed as well as class-literal types
+
+```py
+def _(x: type, y: type[int]):
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: type[int]
+```