vlib: rewrite vlib/v/help, fix print_help_and_exit for sub topics

[ttytm]

Currently, when running v fmt --help it prints:

`v help`: unknown help topic provided. Use `v help` for usage information.
Known help topics: .

This is despite vfmt accepting a help flag and calling the print_help function:

v/cmd/tools/vfmt.v

Lines 90 to 91 in f705897

	if files.len == 0 || '-help' in args || '--help' in args {
	help.print_and_exit('fmt')

This PR fixes it and extends the modules test coverage and better error information.
It is a small module so it was rewritten to improve the module's suboptimalities.

As a note when testing the changes locally: it's required to re-run v self to include when checking out the branch.

🤖 Generated by Copilot at 7a7a403

This pull request refactors and improves the help and help_test modules in the V standard library. It uses new compiler attributes to get the paths to the V executable and the help topics, simplifies the code logic and structure, and adds more test cases.

🤖 Generated by Copilot at 7a7a403

• Refactor the print_and_exit function to use the new attributes and helper functions (link)
• Update the help_test module to use the new attributes and the os.quoted_path function (link, link)
• Rename the test_all_help function to test_all_topics and add two new test functions (link)
• Simplify the logic of getting the topic names from the file paths in test_all_topics (link)

[spytheman]

Excellent work!

The new code is simpler, more robust, and better tested.