Fix local and exported type alias merging (microsoft#36237)

* Fix local and exported type alias merging

* Add baselines

Author: andrewbranch

src/compiler/checker.ts

@@ -29187,7 +29187,7 @@ namespace ts {
             }
         }
 
-        function checkExportsOnMergedDeclarations(node: Node): void {
+        function checkExportsOnMergedDeclarations(node: Declaration): void {
             if (!produceDiagnostics) {
                 return;
             }
@@ -32493,6 +32493,7 @@ namespace ts {
             checkGrammarDecoratorsAndModifiers(node);
 
             checkTypeNameIsReserved(node.name, Diagnostics.Type_alias_name_cannot_be_0);
+            checkExportsOnMergedDeclarations(node);
             checkTypeParameters(node.typeParameters);
             checkSourceElement(node.type);
             registerForUnusedIdentifiersCheck(node);

tests/baselines/reference/typeAliasesDoNotMerge.errors.txt

@@ -0,0 +1,12 @@
+tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts(1,13): error TS2395: Individual declarations in merged declaration 'A' must be all exported or all local.
+tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts(2,6): error TS2395: Individual declarations in merged declaration 'A' must be all exported or all local.
+
+
+==== tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts (2 errors) ====
+    export type A = {}
+                ~
+!!! error TS2395: Individual declarations in merged declaration 'A' must be all exported or all local.
+    type A = {}
+         ~
+!!! error TS2395: Individual declarations in merged declaration 'A' must be all exported or all local.
+    

tests/baselines/reference/typeAliasesDoNotMerge.js

@@ -0,0 +1,8 @@
+//// [typeAliasesDoNotMerge.ts]
+export type A = {}
+type A = {}
+
+
+//// [typeAliasesDoNotMerge.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/typeAliasesDoNotMerge.symbols

@@ -0,0 +1,7 @@
+=== tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts ===
+export type A = {}
+>A : Symbol(A, Decl(typeAliasesDoNotMerge.ts, 0, 0))
+
+type A = {}
+>A : Symbol(A, Decl(typeAliasesDoNotMerge.ts, 0, 0), Decl(typeAliasesDoNotMerge.ts, 0, 18))
+

tests/baselines/reference/typeAliasesDoNotMerge.types

@@ -0,0 +1,7 @@
+=== tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts ===
+export type A = {}
+>A : import("tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge").A
+
+type A = {}
+>A : import("tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge").A
+

tests/cases/conformance/types/typeAliases/typeAliasesDoNotMerge.ts

@@ -0,0 +1,2 @@
+export type A = {}
+type A = {}