[ty] Enums: allow multiple aliases to point to the same member (#20669)

## Summary

closes astral-sh/ty#1293

## Test Plan

Regression test

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/enums.md

@@ -265,6 +265,41 @@ reveal_type(enum_members(Color))
 reveal_type(Color.red)
 ```
 
+Multiple aliases to the same member are also supported. This is a regression test for
+<https://github.com/astral-sh/ty/issues/1293>:
+
+```py
+from ty_extensions import enum_members
+
+class ManyAliases(Enum):
+    real_member = "real_member"
+    alias1 = "real_member"
+    alias2 = "real_member"
+    alias3 = "real_member"
+
+    other_member = "other_real_member"
+
+# revealed: tuple[Literal["real_member"], Literal["other_member"]]
+reveal_type(enum_members(ManyAliases))
+
+reveal_type(ManyAliases.real_member)  # revealed: Literal[ManyAliases.real_member]
+reveal_type(ManyAliases.alias1)  # revealed: Literal[ManyAliases.real_member]
+reveal_type(ManyAliases.alias2)  # revealed: Literal[ManyAliases.real_member]
+reveal_type(ManyAliases.alias3)  # revealed: Literal[ManyAliases.real_member]
+
+reveal_type(ManyAliases.real_member.value)  # revealed: Literal["real_member"]
+reveal_type(ManyAliases.real_member.name)  # revealed: Literal["real_member"]
+
+reveal_type(ManyAliases.alias1.value)  # revealed: Literal["real_member"]
+reveal_type(ManyAliases.alias1.name)  # revealed: Literal["real_member"]
+
+reveal_type(ManyAliases.alias2.value)  # revealed: Literal["real_member"]
+reveal_type(ManyAliases.alias2.name)  # revealed: Literal["real_member"]
+
+reveal_type(ManyAliases.alias3.value)  # revealed: Literal["real_member"]
+reveal_type(ManyAliases.alias3.name)  # revealed: Literal["real_member"]
+```
+
 ### Using `auto()`
 
 ```toml

crates/ty_python_semantic/src/types/enums.rs

@@ -194,12 +194,19 @@ pub(crate) fn enum_metadata<'db>(
             // we don't know if it's a duplicate or not.
             if matches!(
                 value_ty,
-                Type::IntLiteral(_) | Type::StringLiteral(_) | Type::BytesLiteral(_)
+                Type::BooleanLiteral(_)
+                    | Type::IntLiteral(_)
+                    | Type::StringLiteral(_)
+                    | Type::BytesLiteral(_)
             ) {
-                if let Some(previous) = enum_values.insert(value_ty, name.clone()) {
-                    aliases.insert(name.clone(), previous);
+                if let Some(canonical) = enum_values.get(&value_ty) {
+                    // This is a duplicate value, create an alias to the canonical (first) member
+                    aliases.insert(name.clone(), canonical.clone());
                     return None;
                 }
+
+                // This is the first occurrence of this value, track it as the canonical member
+                enum_values.insert(value_ty, name.clone());
             }
 
             let declarations = use_def_map.end_of_scope_symbol_declarations(symbol_id);