Previously, test runner would load tsconfig for each imported file
based on its location, going up the directory tree.
Now, test runner mostly uses a single tsconfig for all imported
files and respects `files`, `include` and `exclude` properties to
determine whether to apply tsconfig to a particular file or not.
For backwards compatibility, root tsconfig is used to load
`playwright.config.ts`, but when `testDir` has its own tsconfig,
it used for loading all tests instead of the root tsconfig.
cb676e29cc