refactor(ivy): ngcc - remove flat-format and use AbsoluteFsPath (#29092)

Now that we are using package.json properties to indicate which
entry-point format to compile, it turns out that we don't really
need to distinguish between flat and non-flat formats, unless we
are compiling `@angular/core`.

PR Close #29092

packages/compiler-cli/ngcc/src/rendering/renderer.ts

@@ -137,7 +137,8 @@ export abstract class Renderer {
 
     if (compiledFile) {
       const importManager = new ImportManager(
-          this.getImportRewriter(this.bundle.src.r3SymbolsFile, this.bundle.isFlat), IMPORT_PREFIX);
+          this.getImportRewriter(this.bundle.src.r3SymbolsFile, this.bundle.isFlatCore),
+          IMPORT_PREFIX);
 
       // TODO: remove constructor param metadata and property decorators (we need info from the
       // handlers to do this)