[red-knot] Narrowing on in tuple[...] and in str (#17059)

## Summary

Part of #13694

Seems there a bit more to cover regarding `in` and other types, but i
can cover them in different PRs

## Test Plan
Add `in.md` file in narrowing conditionals folder

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/in.md

@@ -0,0 +1,80 @@
+# Narrowing for `in` conditionals
+
+## `in` for tuples
+
+```py
+def _(x: int):
+    if x in (1, 2, 3):
+        reveal_type(x)  # revealed: int
+    else:
+        reveal_type(x)  # revealed: int
+```
+
+```py
+def _(x: str):
+    if x in ("a", "b", "c"):
+        reveal_type(x)  # revealed: str
+    else:
+        reveal_type(x)  # revealed: str
+```
+
+```py
+from typing import Literal
+
+def _(x: Literal[1, 2, "a", "b", False, b"abc"]):
+    if x in (1,):
+        reveal_type(x)  # revealed: Literal[1]
+    elif x in (2, "a"):
+        reveal_type(x)  # revealed: Literal[2, "a"]
+    elif x in (b"abc",):
+        reveal_type(x)  # revealed: Literal[b"abc"]
+    elif x not in (3,):
+        reveal_type(x)  # revealed: Literal["b", False]
+    else:
+        reveal_type(x)  # revealed: Never
+```
+
+```py
+def _(x: Literal["a", "b", "c", 1]):
+    if x in ("a", "b", "c", 2):
+        reveal_type(x)  # revealed: Literal["a", "b", "c"]
+    else:
+        reveal_type(x)  # revealed: Literal[1]
+```
+
+## `in` for `str` and literal strings
+
+```py
+def _(x: str):
+    if x in "abc":
+        reveal_type(x)  # revealed: str
+    else:
+        reveal_type(x)  # revealed: str
+```
+
+```py
+from typing import Literal
+
+def _(x: Literal["a", "b", "c", "d"]):
+    if x in "abc":
+        reveal_type(x)  # revealed: Literal["a", "b", "c"]
+    else:
+        reveal_type(x)  # revealed: Literal["d"]
+```
+
+```py
+def _(x: Literal["a", "b", "c", "e"]):
+    if x in "abcd":
+        reveal_type(x)  # revealed: Literal["a", "b", "c"]
+    else:
+        reveal_type(x)  # revealed: Literal["e"]
+```
+
+```py
+def _(x: Literal[1, "a", "b", "c", "d"]):
+    # error: [unsupported-operator]
+    if x in "abc":
+        reveal_type(x)  # revealed: Literal["a", "b", "c"]
+    else:
+        reveal_type(x)  # revealed: Literal[1, "d"]
+```