Add a test for the error line position

[stefnotch]

Issue: #3489

I have tested this in Firefox Nightly (fails, as expected) and Chrome (success, as expected), but not in Safari Technology Preview. I do not have a Macbook available.

What does the "Test have be tested with compatibility mode validation enabled and behave as expected" bullet point mean?

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

When landing this PR, be sure to make any necessary issue status updates.

[stefnotch]

I'm currently not able to easily get a Macbook, so I was hoping that whoever reviews this could either

• verify that the test just passes on Safari
• or, if not, let me know what the output is

[kainino0x]

Sorry I missed this. Will review next week.

[kainino0x]

What does the "Test have be tested with compatibility mode validation enabled and behave as expected" bullet point mean?

in the standalone runner it's listed under "options" which enables ?compatibility=1.

• verify that the test just passes on Safari

It passes! Safari reports linePos=19. (The existing test case
webgpu:api,operation,shader_module,compilation_info:offset_and_length:valid=false;name="unicode" does not pass, but that's unrelated.)

Verified the results in Chrome and Firefox too.

[kainino0x]

LGTM!

[kainino0x]

Thank you for the contribution!