[clang] Use existing AvailabilityKind enum for code completion availability (PR #160296)

[Vlad Serebrennikov via cfe-commits]

================
@@ -3197,12 +3188,47 @@ def __repr__(self) -> str:
         )
 
 
-availabilityKinds = {
-    0: CompletionChunk.Kind("Available"),
-    1: CompletionChunk.Kind("Deprecated"),
-    2: CompletionChunk.Kind("NotAvailable"),
-    3: CompletionChunk.Kind("NotAccessible"),
-}
+# AvailabilityKindCompat is an exact copy of AvailabilityKind, except for __str__
+# This is a temporary measure to keep the string representation the same
+# until we unify the return of CompletionString.availability to be AvailabilityKind
+# Note that deriving from AvailabilityKind directly is not possible
+class AvailabilityKindCompat(BaseEnumeration):
+    """
+    Describes the availability of an entity.
+    """
+
+    # Ensure AvailabilityKindCompat is comparable with AvailabilityKind
+    def __eq__(self, other: object) -> bool:
+        if isinstance(other, AvailabilityKind):
+            return self.value == other.value
+        else:
+            return NotImplemented
----------------
Endilll wrote:

I think it'd be better to first check for precondition, then do the work:
```python
if not isinstance(other, AvailabilityKind):
    return NotImplemented
return self.value == other.value
```
Also, how does this manage to work when two AvailabilityKindCompats are compared?

https://github.com/llvm/llvm-project/pull/160296