fix(ivy): ngtsc program emit ignoring custom transformers

Fixes the `customTransformers` that are passed to the `NgtscProgram.emit` not being passed along.

packages/compiler-cli/src/ngtsc/program.ts

@@ -208,22 +208,31 @@ export class NgtscProgram implements api.Program {
           this.host.writeFile(fileName, data, writeByteOrderMark, onError, sourceFiles);
         };
 
-    const transforms =
+    const customTransforms = opts && opts.customTransformers;
+    const beforeTransforms =
         [ivyTransformFactory(this.compilation !, this.reflector, this.coreImportsFrom)];
+    const afterTransforms = customTransforms && customTransforms.afterTs || [];
+
     if (this.factoryToSourceInfo !== null) {
-      transforms.push(generatedFactoryTransform(this.factoryToSourceInfo, this.coreImportsFrom));
+      beforeTransforms.push(
+          generatedFactoryTransform(this.factoryToSourceInfo, this.coreImportsFrom));
     }
     if (this.isCore) {
-      transforms.push(ivySwitchTransform);
+      beforeTransforms.push(ivySwitchTransform);
+    }
+    if (customTransforms && customTransforms.beforeTs) {
+      beforeTransforms.push(...customTransforms.beforeTs);
     }
+
     // Run the emit, including a custom transformer that will downlevel the Ivy decorators in code.
     const emitResult = emitCallback({
       program: this.tsProgram,
       host: this.host,
       options: this.options,
       emitOnlyDtsFiles: false, writeFile,
       customTransformers: {
-        before: transforms,
+        before: beforeTransforms,
+        after: afterTransforms,
       },
     });
     return emitResult;