perf: latest tsickle to tree shake: abstract class methods & interfaces (#18236)

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

packages/compiler/src/expression_parser/lexer.ts

@@ -231,7 +231,6 @@ class _Scanner {
    * @param two second symbol (part of the operator when the second code point matches)
    * @param threeCode code point for the third symbol
    * @param three third symbol (part of the operator when provided and matches source expression)
-   * @returns {Token}
    */
   scanComplexOperator(
       start: number, one: string, twoCode: number, two: string, threeCode?: number,