We now create 2 programs with exactly the same fileNames and
exactly the same `import` / `export` declarations,
allowing TS to reuse the structure of first program
completely. When passing in an oldProgram and the files didn’t change,
TS can also reuse the old program completely.
This is possible buy adding generated files to TS
in `host.geSourceFile` via `ts.SourceFile.referencedFiles`.
This commit also:
- has a minor side effect on how we generate shared stylesheets:
- previously every import in a stylesheet would generate a new
`.ngstyles.ts` file.
- now, we only generate 1 `.ngstyles.ts` file per entry in `@Component.styleUrls`.
This was required as we need to be able to determine the program files
without loading the resources (which can be async).
- makes all angular related methods in `CompilerHost`
optional, allowing to just use a regular `ts.CompilerHost` as `CompilerHost`.
- simplifies the logic around `Compiler.analyzeNgModules` by introducing `NgAnalyzedFile`.
Perf impact: 1.5s improvement in compiling angular io
PR Close#19275
