fix(@angular/build): skip semantic diagnostics for declaration files

Declaration files don't produce semantic or template diagnostics, so
calling getSemanticDiagnostics() on them was just wasted work. Move
the isDeclarationFile guard to before that call so .d.ts files are
skipped entirely.

Author: arturovt

packages/angular/build/src/tools/angular/compilation/aot-compilation.ts

@@ -265,17 +265,17 @@ export class AotCompilation extends AngularCompilation {
         continue;
       }
 
+      // Declaration files have no semantic or template diagnostics.
+      if (sourceFile.isDeclarationFile) {
+        continue;
+      }
+
       yield* profileSync(
         'NG_DIAGNOSTICS_SEMANTIC',
         () => typeScriptProgram.getSemanticDiagnostics(sourceFile),
         true,
       );
 
-      // Declaration files cannot have template diagnostics
-      if (sourceFile.isDeclarationFile) {
-        continue;
-      }
-
       // Only request Angular template diagnostics for affected files to avoid
       // overhead of template diagnostics for unchanged files.
       if (affectedFiles.has(sourceFile)) {