feat: explicitly ban --isolatedModules --preserveConstEnums false

Author: FauxFaux

src/compiler/diagnosticMessages.json

@@ -3789,6 +3789,10 @@
         "category": "Error",
         "code": 5090
     },
+    "Option 'isolatedModules' requires 'preserveConstEnum', as constants are not inlined in this mode.": {
+        "category": "Error",
+        "code": 5091
+    },
 
     "Generates a sourcemap for each corresponding '.d.ts' file.": {
         "category": "Message",

src/compiler/program.ts

@@ -3156,6 +3156,10 @@ namespace ts {
                     createDiagnosticForOptionName(Diagnostics.Option_isolatedModules_can_only_be_used_when_either_option_module_is_provided_or_option_target_is_ES2015_or_higher, "isolatedModules", "target");
                 }
 
+                if (options.preserveConstEnums === false) {
+                    createDiagnosticForOptionName(Diagnostics.Option_isolatedModules_requires_preserveConstEnum_as_constants_are_not_inlined_in_this_mode, "isolatedModules", "preserveConstEnums");
+                }
+
                 const firstNonExternalModuleSourceFile = find(files, f => !isExternalModule(f) && !isSourceFileJS(f) && !f.isDeclarationFile && f.scriptKind !== ScriptKind.JSON);
                 if (firstNonExternalModuleSourceFile) {
                     const span = getErrorSpanForNode(firstNonExternalModuleSourceFile, firstNonExternalModuleSourceFile);