test_runner: preserve literal directory arguments

[repzakske]

An existing directory passed to node --test is expanded by appending the default test glob to its path. Glob metacharacters in the directory name then become active: node --test 'tests[1]' can skip its tests or run tests from a sibling named tests1.

Search from the directory itself so its path stays outside the glob pattern. Preserve explicit glob handling, node_modules filtering, and report paths, while de-duplicating overlapping selections.

Extend the existing CLI directory tests to cover bracket and brace names, trailing separators, and a sibling collision in both isolation modes.

Validation:

• Built Node v27.0.0-pre from source on Linux x64 with GCC 14 and --v8-disable-temporal-support.
• The CLI regression and all 84 remaining parallel/sequential test-runner files passed.
• Repository ESLint passed for both changed files.

Assisted-by: Codex

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[github-actions]

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