refactor(compiler): simplify the CompilerHost used for transformers

- remove unneeded methods (`getNgCanonicalFileName`, `assumeFileExists`)
- simplify moduleName <-> fileName conversion logic as we don’t need to
  account for `genDir` anymore.
- rename `createNgCompilerHost` -> `createCompilerHost`

packages/compiler/src/aot/static_reflector.ts

@@ -82,12 +82,11 @@ export class StaticReflector implements CompileReflector {
   }
 
   resolveExternalReference(ref: o.ExternalReference): StaticSymbol {
-    const importSymbol = this.getStaticSymbol(ref.moduleName !, ref.name !);
-    const rootSymbol = this.findDeclaration(ref.moduleName !, ref.name !);
-    if (importSymbol != rootSymbol) {
-      this.symbolResolver.recordImportAs(rootSymbol, importSymbol);
-    }
-    return rootSymbol;
+    const refSymbol = this.symbolResolver.getSymbolByModule(ref.moduleName !, ref.name !);
+    const declarationSymbol = this.findSymbolDeclaration(refSymbol);
+    this.symbolResolver.recordModuleNameForFileName(refSymbol.filePath, ref.moduleName !);
+    this.symbolResolver.recordImportAs(declarationSymbol, refSymbol);
+    return declarationSymbol;
   }
 
   findDeclaration(moduleUrl: string, name: string, containingFile?: string): StaticSymbol {

packages/compiler/src/aot/static_symbol_resolver.ts

@@ -172,6 +172,10 @@ export class StaticSymbolResolver {
     this.importAs.set(sourceSymbol, targetSymbol);
   }
 
+  recordModuleNameForFileName(fileName: string, moduleName: string) {
+    this.knownFileNameToModuleNames.set(fileName, moduleName);
+  }
+
   /**
    * Invalidate all information derived from the given file.
    *