Handle rebuild failures without exiting

When a rebuild fails, mark it as a builder failure so the watcher doesn't re-throw it, causing it to be an unhandled error that results in the process exiting.

Fixes #9584

lib/models/builder.js

@@ -221,6 +221,10 @@ class Builder extends CoreObject {
     } catch (error) {
       await this.processAddonBuildSteps('buildError', error);
 
+      // Mark this as a builder error so the watcher knows it has been handled
+      // and won't re-throw it
+      error.isBuilderError = true;
+
       throw error;
     } finally {
       clearInterval(uiProgressIntervalID);

tests/unit/models/builder-test.js

@@ -478,6 +478,20 @@ describe('models/builder.js', function () {
       await expect(builder.build()).to.be.rejected;
       expect(hooksCalled).to.deep.equal(['preBuild', 'build', 'postBuild', 'outputReady', 'buildError']);
     });
+
+    it('sets `isBuilderError` on handled addon errors', async function () {
+      addon.postBuild = function () {
+        return Promise.reject(new Error('preBuild Error'));
+      };
+
+      let error;
+      try {
+        await builder.build();
+      } catch (e) {
+        error = e;
+      }
+      expect(error).to.haveOwnProperty('isBuilderError', true);
+    });
   });
 
   describe('fallback from broccoli 2 to broccoli-builder', function () {