feat(ivy): add ngcc ivy switch (#25238)

Provides a runtime and compile time switch for ivy including
`ApplicationRef.bootstrapModule`.

This is done by naming the symbols such that `ngcc` (angular
Compatibility compiler) can rename symbols in such a way that running
`ngcc` command will switch the `@angular/core` module from `legacy` to
`ivy` mode.

This is done as follows:

```
const someToken__PRE_NGCC__ = ‘legacy mode’;
const someToken__POST_NGCC__ = ‘ivy mode’;

export someSymbol = someToken__PRE_NGCC__;
```

The `ngcc` will search for any token which ends with `__PRE_NGCC__`
and replace it with `__POST_NGCC__`. This allows the `@angular/core`
package to be rewritten to ivy mode post `ngcc` execution.

PR Close #25238

packages/compiler/test/schema/schema_extractor.ts

@@ -38,7 +38,9 @@ const MISSING_FROM_CHROME: {[el: string]: string[]} = {
   ':svg:cursor^:svg:': [],
 };
 
-const _G: any = global;
+const _G: any = typeof window != 'undefined' && window || typeof global != 'undefined' && global ||
+    typeof self != 'undefined' && self;
+
 const document: any = typeof _G['document'] == 'object' ? _G['document'] : null;
 
 export function extractSchema(): Map<string, string[]>|null {