Fix angular build with correct resolving referenced modules

[GDreyV]

Instead of creating stub file provide valid browser alias.
Initial issue #523
Updated issue #631

[tomlongridge]

@GDreyV - are you able to provide a repro case for this? I've tried it with both Bugsnag Angular example (upgraded to 7.2.0) and the Angular basic example (https://angular.io/start) with Bugsnag added and neither result in the error you are seeing.

We need reproduction instructions/project to make this PR something we can release.

[GDreyV]

Here's the test repository to reproduce the problem: https://github.com/GDreyV/bugsnag-angular-test
To be sure that we are on the same page I used following steps to reproduce the issue:

npm list -g --depth=0
+-- @angular/[email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
+-- [email protected]
`-- [email protected]

ng new bugsnag-test
cd bugsnag-test
npm install --save @bugsnag/js @bugsnag/core @bugsnag/plugin-angular

update app.module.ts with bugsnag init

ng build --eval-source-map --prod --aot
ERROR in ./node_modules/@bugsnag/browser/dist/types/bugsnag.ts
Module build failed (from ./node_modules/@ngtools/webpack/src/index.js):
Error: d:\Work\Sympli\figma\bugsnag\case\bugsnag-test\node_modules\@bugsnag\browser\dist\types\bugsnag.ts is missing from the TypeScript compilation. Please make sure it is in your tsconfig via the 'files' or 'include' property.
The missing file seems to be part of a third party library. TS files in published libraries are often a sign of a badly packaged library. Please open an issue in the library repository to alert its author and ask them to package the library using the Angular Package Format (https://goo.gl/jB3GVv).

[tomlongridge]

Reviewed and tested it - this looks good. Merging changes via #633.

Thanks @GDreyV !