Secondary entry points (testing, static, etc) are rolled up into a
single ESM/ES2015 file, then downleveled to ESM/ES2015. This downleveling
was not working and was producing ESM/ES2015. Also, the @angular/core
package's .babelrc file was missing reference to Rx Observable which
broke the UMD bundle.
Fixes#14730
TypeScript compiler will now build to ES2015 code and modules. Babili is used to minify ES2015
code, providing an initial optimization that we couldn't previously get just from Uglify. Uses
Babel to convert ES2015 to UMD/ES5 code, and Uglify to minimize the output.
Jason Aden
Jason Aden