refactor(@angular-devkit/build-angular): use library output for stylesheet child compilations
refactor(@angular-devkit/build-angular): use library output for stylesheet child compilations

This change allows the result of the stylesheet Webpack compilation to be explicitly available for access after the output source code is generated.  The previous method relied on assumptions within the code generated by Webpack and no longer worked with Webpack 5.

clydin/angular-cli,ocombe/angular-cli,clydin/angular-cli,Brocco/angular-cli,Brocco/angular-cli,geofffilippi/angular-cli,catull/angular-cli,ocombe/angular-cli,angular/angular-cli,Brocco/angular-cli,ocombe/angular-cli,ocombe/angular-cli,angular/angular-cli,ocombe/angular-cli,catull/angular-cli,clydin/angular-cli,Brocco/angular-cli,geofffilippi/angular-cli,catull/angular-cli,catull/angular-cli,clydin/angular-cli,angular/angular-cli,geofffilippi/angular-cli,angular/angular-cli,Brocco/angular-cli,geofffilippi/angular-cli