Respond to code review comments

Author: mhegazy

src/compiler/core.ts

@@ -1710,7 +1710,7 @@ namespace ts {
         return moduleResolution;
     }
 
-    export function getStrictOptionValue(compilerOptions: CompilerOptions, flag: "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "alwaysStrict"): boolean {
+    export function getStrictOptionValue(compilerOptions: CompilerOptions, flag: StrictOptionName): boolean {
         return compilerOptions[flag] === undefined ? compilerOptions.strict : compilerOptions[flag];
     }
 

src/compiler/types.ts

@@ -3676,6 +3676,8 @@ namespace ts {
 
     export type CompilerOptionsValue = string | number | boolean | (string | number)[] | string[] | MapLike<string[]> | PluginImport[] | null | undefined;
 
+    export type StrictOptionName = "noImplicitAny" | "noImplicitThis" | "strictNullChecks" | "strictFunctionTypes" | "alwaysStrict";
+
     export interface CompilerOptions {
         /*@internal*/ all?: boolean;
         allowJs?: boolean;