…ipt 5.0 (#49492)

Previously, attempting to turn off the `experimentalDecorators` TypeScript configuration
option within an Angular project would result in build time errors. These errors were due
to an exposed Decorator signature from `@angular/core` that TypeScript thought was incompatible
with standard decorators. However, Angular's class decorators (`Component`, `Directive`, `Pipe`,
`Injectable`, `NgModule`) are actually already compatible with standard decorators. The export types for
the decorators only needed to be updated to reflect that compatibility. With the updated exported types,
applications will now successfully compile and execute in AOT mode with one important dependency injection
caveat explained in the note below.
For JIT mode applications that are built with the Angular CLI, `@ngtools/webpack`, or use `tsickle`,
there were also no additional changes required. These tools automatically convert property decorators
(now called field decorators) at build time to store Angular property metadata directly on the relevant
class. Building with these tools is the overwhelmingly common method of building an application. Any
applications that do not use one of these tools will not function at runtime in JIT mode if using standard
decorators. The behavior and code for when experimental decorators is enabled has been left intact.

NOTE: Angular constructor dependency injection that requires parameter decorators is not supported.
The standard decorator specification does not support parameter decorators. The `inject` function must be
used for all cases that previously required a parameter decorator. This includes such decorators as `Inject`,
`Optional`, `Self`, `SkipSelf`, `Host`, and `Attribute`. Constructor dependency injection that relies only
on the supplied parameter type will continue to function as expected if using AOT; as well as in JIT mode
if using the Angular CLI, `@ngtools/webpack` directly, or `tsickle`.

Documentation for the `inject` function can be found at: https://angular.io/api/core/inject
The decorator specification proposal can be found at: https://github.com/tc39/proposal-decorators

PR Close #49492