feat(compiler-cli): add support to extend angularCompilerOptions (#22717)

`TypeScript` only supports merging and extending of `compilerOptions`. This is an implementation to support extending and inheriting of `angularCompilerOptions` from multiple files.

Closes: #22684

PR Close #22717

packages/compiler-cli/src/perform_compile.ts

@@ -128,7 +128,37 @@ export function readConfiguration(
   try {
     const {projectFile, basePath} = calcProjectFileAndBasePath(project);
 
-    let {config, error} = ts.readConfigFile(projectFile, ts.sys.readFile);
+    const readExtendedConfigFile =
+        (configFile: string, existingConfig?: any): {config?: any, error?: ts.Diagnostic} => {
+          const {config, error} = ts.readConfigFile(configFile, ts.sys.readFile);
+
+          if (error) {
+            return {error};
+          }
+
+          // we are only interested into merging 'angularCompilerOptions' as
+          // other options like 'compilerOptions' are merged by TS
+          const baseConfig = existingConfig || config;
+          if (existingConfig) {
+            baseConfig.angularCompilerOptions = {...config.angularCompilerOptions,
+                                                 ...baseConfig.angularCompilerOptions};
+          }
+
+          if (config.extends) {
+            let extendedConfigPath = path.resolve(path.dirname(configFile), config.extends);
+            extendedConfigPath = path.extname(extendedConfigPath) ? extendedConfigPath :
+                                                                    `${extendedConfigPath}.json`;
+
+            if (fs.existsSync(extendedConfigPath)) {
+              // Call read config recursively as TypeScript only merges CompilerOptions
+              return readExtendedConfigFile(extendedConfigPath, baseConfig);
+            }
+          }
+
+          return {config: baseConfig};
+        };
+
+    const {config, error} = readExtendedConfigFile(projectFile);
 
     if (error) {
       return {