TS 5.0 allows `"extends": ["./a", "./b"]`. _read_tsconfig_aliases called
`extends.startswith("@")` directly, so an array raised
`AttributeError: 'list' object has no attribute 'startswith'`. _safe_extract
caught it and skipped the WHOLE file — and since alias resolution fires on any
path-aliased import, every TS file using `@/`-style imports in a repo with
array-extends tsconfig was dropped, yielding an empty graph.
Normalize `extends` to a list (str -> [str], list kept, else []), process
entries in order (later overrides earlier, current config's paths override all
parents per TS semantics), and skip scoped npm configs (`@...`) per entry as
before.
Adds regression test test_tsconfig_array_extends_alias_resolves_existing_ts_file.
msotnikov
336652779b