In previous version of tsickle abstract class methods were materialized.
The change resulted in 6Kb savings in angular.io bundle.
This change also required the removal of `@private` and `@return` type
annotation as it is explicitly dissalowed by tsickle.
NOTE: removed casts in front of `makeDecorator` due to:
https://github.com/angular/devkit/issues/45
```
14938 Jul 19 13:16 0.b19e913fbdd6507d346b.chunk.js
1535 Jul 19 13:16 inline.d8e019ea3cfdd86c2bd0.bundle.js
589178 Jul 19 13:16 main.54c97bcb6f254776b678.bundle.js
34333 Jul 19 13:16 polyfills.4a3c9ca9481d53803157.bundle.js
14938 Jul 18 16:55 0.b19e913fbdd6507d346b.chunk.js
1535 Jul 18 16:55 inline.0c83abb44fad9a2768a7.bundle.js
582786 Jul 18 16:55 main.ea290db71b051813e156.bundle.js
34333 Jul 18 16:55 polyfills.4a3c9ca9481d53803157.bundle.js
main savings: 589178 - 582786 = 6,392
```
PR Close#18236
HttpClient is an evolution of the existing Angular HTTP API, which exists
alongside of it in a separate package, @angular/common/http. This structure
ensures that existing codebases can slowly migrate to the new API.
The new API improves significantly on the ergonomics and features of the legacy
API. A partial list of new features includes:
* Typed, synchronous response body access, including support for JSON body types
* JSON is an assumed default and no longer needs to be explicitly parsed
* Interceptors allow middleware logic to be inserted into the pipeline
* Immutable request/response objects
* Progress events for both request upload and response download
* Post-request verification & flush based testing framework
`flush()` can now be used from within fakeAsync tests to simulate moving
time forward until all macrotask events have been cleared from the
event queue.
Previous to 2.x there were some source maps distrubted, but they didn't go
all the way back to the TypeScript sources and they weren't available for
all JavaScript distrubted to NPM.
With this change source maps will be available for FESM distributions as
well as UMD and will go all the way back to TypeScript sources.
Fixes#15184
