fix: revive schematics functionality

[Den-dp]

Include ignored builders.json and schematics.json files into package so ng add
will stop complain about missing collections.

Closes: #226

[Den-dp]

despite the fact that this PR helps with ng add, I just found another problem while running spa build

ENOENT: no such file or directory, open 'C:\dev\rep\testapp\node_modules\single-spa-angular\src\builders\browser\schema.json'
Error: ENOENT: no such file or directory, open 'C:\dev\rep\testapp\node_modules\single-spa-angular\src\builders\browser\schema.json'
    at Object.openSync (fs.js:440:3)
    at Object.readFileSync (fs.js:342:35)
    at Observable._subscribe (C:\dev\rep\testapp\node_modules\@angular\cli\node_modules\@angular-devkit\core\node\host.js:171:35)
    at Observable._trySubscribe (C:\dev\rep\testapp\node_modules\@angular\cli\node_modules\rxjs\internal\Observable.js:44:25)
    at Observable.subscribe (C:\dev\rep\testapp\node_modules\@angular\cli\node_modules\rxjs\internal\Observable.js:30:22)
    at MapOperator.call (C:\dev\rep\testapp\node_modules\@angular-devkit\architect\node_modules\rxjs\internal\operators\map.js:32:23)
    at Observable.subscribe (C:\dev\rep\testapp\node_modules\@angular\cli\node_modules\rxjs\internal\Observable.js:25:22)

It looks like we should add all schema.json files from src/. Will try it right now and add to this PR if it will help

[Den-dp]

Changing "src/schematics/ng-add/schema.json" -> "src/**/schema.json" helped

[joeldenning]

Released in https://github.com/single-spa/single-spa-angular/releases/tag/v3.5.3