Quick preemtive bugfix and dead code removal

Author: weswigham

src/compiler/parser.ts

@@ -102,6 +102,7 @@ import {
     FunctionOrConstructorTypeNode,
     FunctionTypeNode,
     GetAccessorDeclaration,
+    getBaseFileName,
     getBinaryOperatorPrecedence,
     getFullWidth,
     getJSDocCommentRanges,
@@ -10097,7 +10098,7 @@ namespace IncrementalParser {
 
 /** @internal */
 export function isDeclarationFileName(fileName: string): boolean {
-    return fileExtensionIsOneOf(fileName, supportedDeclarationExtensions) || (fileExtensionIs(fileName, Extension.Ts) && stringContains(fileName, ".d."));
+    return fileExtensionIsOneOf(fileName, supportedDeclarationExtensions) || (fileExtensionIs(fileName, Extension.Ts) && stringContains(getBaseFileName(fileName), ".d."));
 }
 
 /** @internal */

src/compiler/utilities.ts

@@ -8198,8 +8198,6 @@ export const supportedJSExtensions: readonly Extension[][] = [[Extension.Js, Ext
 /** @internal */
 export const supportedJSExtensionsFlat: readonly Extension[] = flatten(supportedJSExtensions);
 const allSupportedExtensions: readonly Extension[][] = [[Extension.Ts, Extension.Tsx, Extension.Dts, Extension.Js, Extension.Jsx], [Extension.Cts, Extension.Dcts, Extension.Cjs], [Extension.Mts, Extension.Dmts, Extension.Mjs]];
-/** @internal */
-export const allSupportedExtensionsFlat = flatten(allSupportedExtensions);
 const allSupportedExtensionsWithJson: readonly Extension[][] = [...allSupportedExtensions, [Extension.Json]];
 /** @internal */
 export const supportedDeclarationExtensions: readonly Extension[] = [Extension.Dts, Extension.Dcts, Extension.Dmts];