fix(ngcc): correctly detect external files from nested node_modules/ (#36559)

Previously, when we needed to detect whether a file is external to a
package, we only checked whether the relative path to the file from the
package's root started with `..`. This would detect external imports
when the packages were siblings (e.g. peer dependencies or hoisted to
the top of `node_modules/` by the package manager), but would fail to
detect imports from packages located in nested `node_modules/` as
external. For example, importing `node_modules/foo/node_modules/bar`
from a file in `node_modules/foo/` would be considered internal to the
`foo` package.

This could result in processing/analyzing more files than necessary.
More importantly it could lead to errors due to trying to analyze
non-Angular packages that were direct dependencies of Angular packages.

This commit fixes it by also verifying that the relative path to a file
does not start with `node_modules/`.

Jira issue: [FW-2068](https://angular-team.atlassian.net/browse/FW-2068)

Fixes #36526

PR Close #36559

packages/compiler-cli/ngcc/src/analysis/util.ts

@@ -11,7 +11,8 @@ import {absoluteFromSourceFile, AbsoluteFsPath, relative} from '../../../src/ngt
 import {DependencyTracker} from '../../../src/ngtsc/incremental/api';
 
 export function isWithinPackage(packagePath: AbsoluteFsPath, sourceFile: ts.SourceFile): boolean {
-  return !relative(packagePath, absoluteFromSourceFile(sourceFile)).startsWith('..');
+  const relativePath = relative(packagePath, absoluteFromSourceFile(sourceFile));
+  return !relativePath.startsWith('..') && !relativePath.startsWith('node_modules/');
 }
 
 class NoopDependencyTracker implements DependencyTracker {