Do not merge commonJS exports into an alias (microsoft#28133)

* Do not merge commonsjs exports onto an alias

getCommonJSExportEquals merges export assignments and export property
assignments. Something like this, which has no equivalent structure in
TS:

```js
module.exports = function() { }
module.exports.expando = 1
```

However, it is sometimes called with an alias, when its
parent, resolveExternalModuleSymbol, is called with dontResolveAlias:
true, and when the initialiser of the export assignment is an alias:

```js
function alias() { }
module.exports = alias
module.exports.expando = 1
```

In this case, (1) the actual value `alias` will have already merged in a
previous call to getCommonJSExportEquals and
(2) getTypeOfSymbol will follow the alias symbol to get the right type.
So getCommonJSExportEquals should do nothing in this case.

This bug manifests in the code for dynamic imports, which calls
getTypeOfSymbol on the incorrectly merged alias, which now has enough
value flags--Function, for example--to take the wrong branch and
subsequently crash.

* Update baselines

Author: sandersn

src/compiler/checker.ts

@@ -2362,7 +2362,7 @@ namespace ts {
         }
 
         function getCommonJsExportEquals(exported: Symbol | undefined, moduleSymbol: Symbol): Symbol | undefined {
-            if (!exported || exported === unknownSymbol || exported === moduleSymbol || moduleSymbol.exports!.size === 1) {
+            if (!exported || exported === unknownSymbol || exported === moduleSymbol || moduleSymbol.exports!.size === 1 || exported.flags & SymbolFlags.Alias) {
                 return exported;
             }
             const merged = cloneSymbol(exported);

tests/baselines/reference/errorForConflictingExportEqualsValue.types

@@ -6,6 +6,6 @@ export = x;
 >x : any
 
 import("./a");
->import("./a") : Promise<typeof import("/a").x>
+>import("./a") : Promise<any>
 >"./a" : "./a"
 

tests/baselines/reference/moduleExportAliasImported.symbols

@@ -0,0 +1,19 @@
+=== tests/cases/conformance/salsa/bug28014.js ===
+exports.version = 1
+>exports.version : Symbol(version)
+>exports : Symbol(version, Decl(bug28014.js, 0, 0))
+>version : Symbol(version, Decl(bug28014.js, 0, 0))
+
+function alias() { }
+>alias : Symbol(alias, Decl(bug28014.js, 0, 19))
+
+module.exports = alias
+>module.exports : Symbol("tests/cases/conformance/salsa/bug28014", Decl(bug28014.js, 0, 0))
+>module : Symbol(export=, Decl(bug28014.js, 1, 20))
+>exports : Symbol(export=, Decl(bug28014.js, 1, 20))
+>alias : Symbol(alias, Decl(bug28014.js, 0, 19))
+
+=== tests/cases/conformance/salsa/importer.js ===
+import('./bug28014')
+>'./bug28014' : Symbol("tests/cases/conformance/salsa/bug28014", Decl(bug28014.js, 0, 0))
+

tests/baselines/reference/moduleExportAliasImported.types

@@ -0,0 +1,23 @@
+=== tests/cases/conformance/salsa/bug28014.js ===
+exports.version = 1
+>exports.version = 1 : 1
+>exports.version : number
+>exports : typeof alias
+>version : number
+>1 : 1
+
+function alias() { }
+>alias : typeof alias
+
+module.exports = alias
+>module.exports = alias : typeof alias
+>module.exports : typeof alias
+>module : { "tests/cases/conformance/salsa/bug28014": typeof alias; }
+>exports : typeof alias
+>alias : typeof alias
+
+=== tests/cases/conformance/salsa/importer.js ===
+import('./bug28014')
+>import('./bug28014') : Promise<() => void>
+>'./bug28014' : "./bug28014"
+

tests/cases/conformance/salsa/moduleExportAliasImported.ts

@@ -0,0 +1,12 @@
+// @allowJs: true
+// @noEmit: true
+// @checkJs: true
+// @target: esnext
+// @module: esnext
+// @Filename: bug28014.js
+exports.version = 1
+function alias() { }
+module.exports = alias
+
+// @Filename: importer.js
+import('./bug28014')