fix(spectacular): expose SpectacularFeatureTestingRootModule to prevent NGCC error when using Nx

[LayZeeDK]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

When using Nx and Yarn, NGCC fails after adding Spectacular.

Issue Number: N/A

What is the new behavior?

No NGCC error when using Nx and Yarn to install Spectacular.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

NGCC error message when

node ./decorate-angular-cli.js && ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points

is run:

Error: Error on worker #4: Error: No typings declaration can be found for the referenced NgModule class in static withFeature({ featureModule, featurePath, routerOptions = {}, }) {
        const { providers: routerTestingProviders = [], } = RouterTestingModule.withRoutes([{ path: featurePath, loadChildren: () => featureModule }], routerOptions);
        return {
            ngModule: SpectacularFeatureTestingRootModule,
            providers: [
                ...routerTestingProviders,
                {
                    provide: featurePathToken,
                    useValue: featurePath,
                },
            ],
        };
    }.
    at ModuleWithProvidersAnalyzer.resolveNgModuleReference (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\analysis\module_with_providers_analyzer.js:179:23)
    at ModuleWithProvidersAnalyzer.getDtsModuleWithProvidersFunction (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\analysis\module_with_providers_analyzer.js:166:33)
    at C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\analysis\module_with_providers_analyzer.js:47:43    
    at Array.forEach (<anonymous>)
    at C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\analysis\module_with_providers_analyzer.js:40:28    
    at Array.forEach (<anonymous>)
    at ModuleWithProvidersAnalyzer.analyzeProgram (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\analysis\module_with_providers_analyzer.js:38:23)
    at Transformer.analyzeProgram (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\packages\transformer.js:133:45)
    at Transformer.transform (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\packages\transformer.js:76:27)
    at C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\execution\create_compile_function.js:52:42
    at ClusterMaster.onWorkerMessage (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\execution\cluster\master.js:195:27)
    at C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\execution\cluster\master.js:55:95
    at ClusterMaster.<anonymous> (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\execution\cluster\master.js:293:57)
    at step (C:\projects\sandbox\nx114-angular-app\node_modules\tslib\tslib.js:143:27)
    at Object.next (C:\projects\sandbox\nx114-angular-app\node_modules\tslib\tslib.js:124:57)
    at C:\projects\sandbox\nx114-angular-app\node_modules\tslib\tslib.js:117:75
    at new Promise (<anonymous>)
    at Object.__awaiter (C:\projects\sandbox\nx114-angular-app\node_modules\tslib\tslib.js:113:16)
    at EventEmitter.<anonymous> (C:\projects\sandbox\nx114-angular-app\node_modules\@angular\compiler-cli\ngcc\src\execution\cluster\master.js:287:32)
    at EventEmitter.emit (events.js:314:20)

[santoshyadavdev]

LGTM