Fix alias of module.exports->exports->IIFE (#27992)

In JS, when you assign `module.exports = exports` and the entire module is
wrapped in an IIFE, the resulting `export=` symbol, after following
aliases, is the module itself. This results in trying to merge the
file's exports with itself inside `getCommonJsExportEquals`, since it
thinks that it has found new exports, possibly in an object literal,
that need to be merged with the file's exports.

For example:

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

src/compiler/checker.ts

@@ -2353,11 +2353,16 @@ namespace ts {
         function resolveExternalModuleSymbol(moduleSymbol: Symbol, dontResolveAlias?: boolean): Symbol;
         function resolveExternalModuleSymbol(moduleSymbol: Symbol | undefined, dontResolveAlias?: boolean): Symbol | undefined;
         function resolveExternalModuleSymbol(moduleSymbol: Symbol, dontResolveAlias?: boolean): Symbol {
-            return moduleSymbol && getMergedSymbol(getCommonJsExportEquals(resolveSymbol(moduleSymbol.exports!.get(InternalSymbolName.ExportEquals), dontResolveAlias), moduleSymbol)) || moduleSymbol;
+            if (moduleSymbol) {
+                const exportEquals = resolveSymbol(moduleSymbol.exports!.get(InternalSymbolName.ExportEquals), dontResolveAlias);
+                const exported = getCommonJsExportEquals(exportEquals, moduleSymbol);
+                return getMergedSymbol(exported) || moduleSymbol;
+            }
+            return undefined!;
         }
 
         function getCommonJsExportEquals(exported: Symbol | undefined, moduleSymbol: Symbol): Symbol | undefined {
-            if (!exported || exported === unknownSymbol || moduleSymbol.exports!.size === 1) {
+            if (!exported || exported === unknownSymbol || exported === moduleSymbol || moduleSymbol.exports!.size === 1) {
                 return exported;
             }
             const merged = cloneSymbol(exported);

tests/baselines/reference/moduleExportAliasExports.symbols

@@ -0,0 +1,21 @@
+=== tests/cases/conformance/salsa/Eloquent.js ===
+// bug #27365, crashes from github.com/marijnh/Eloquent-JavaScript
+(function() {
+exports.bigOak = 1
+>exports.bigOak : Symbol(bigOak, Decl(Eloquent.js, 1, 13))
+>exports : Symbol(bigOak, Decl(Eloquent.js, 1, 13))
+>bigOak : Symbol(bigOak, Decl(Eloquent.js, 1, 13))
+
+exports.everywhere = 2
+>exports.everywhere : Symbol(everywhere, Decl(Eloquent.js, 2, 18))
+>exports : Symbol(everywhere, Decl(Eloquent.js, 2, 18))
+>everywhere : Symbol(everywhere, Decl(Eloquent.js, 2, 18))
+
+module.exports = exports
+>module.exports : Symbol("tests/cases/conformance/salsa/Eloquent", Decl(Eloquent.js, 0, 0))
+>module : Symbol(export=, Decl(Eloquent.js, 3, 22))
+>exports : Symbol(export=, Decl(Eloquent.js, 3, 22))
+>exports : Symbol("tests/cases/conformance/salsa/Eloquent", Decl(Eloquent.js, 0, 0))
+
+})()
+

tests/baselines/reference/moduleExportAliasExports.types

@@ -0,0 +1,30 @@
+=== tests/cases/conformance/salsa/Eloquent.js ===
+// bug #27365, crashes from github.com/marijnh/Eloquent-JavaScript
+(function() {
+>(function() {exports.bigOak = 1exports.everywhere = 2module.exports = exports})() : void
+>(function() {exports.bigOak = 1exports.everywhere = 2module.exports = exports}) : () => void
+>function() {exports.bigOak = 1exports.everywhere = 2module.exports = exports} : () => void
+
+exports.bigOak = 1
+>exports.bigOak = 1 : 1
+>exports.bigOak : number
+>exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+>bigOak : number
+>1 : 1
+
+exports.everywhere = 2
+>exports.everywhere = 2 : 2
+>exports.everywhere : number
+>exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+>everywhere : number
+>2 : 2
+
+module.exports = exports
+>module.exports = exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+>module.exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+>module : { "tests/cases/conformance/salsa/Eloquent": typeof import("tests/cases/conformance/salsa/Eloquent"); }
+>exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+>exports : typeof import("tests/cases/conformance/salsa/Eloquent")
+
+})()
+

tests/cases/conformance/salsa/moduleExportAliasExports.ts

@@ -0,0 +1,10 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @Filename: Eloquent.js
+// bug #27365, crashes from github.com/marijnh/Eloquent-JavaScript
+(function() {
+exports.bigOak = 1
+exports.everywhere = 2
+module.exports = exports
+})()