Investigate accessible name fallback after valid but empty aria-labelledby

[Jym77]

https://act-rules.github.io/rules/ffd0e9#failed-example-1

<span id="label"></span>
<h1 aria-labelledby="label">ACT rules</h1>

The IDref does exist but when processing it for name results in an empty name.
It is not fully clear in the specs that step 2B should continue in that case (if the IDref exists, it is processed and returned, comparatively step 2C is explicit about aria-label not being empty).

In our current implementation, that step returns an empty value and fromSteps thus continue to the next step.
See also act-rules/act-rules.github.io#1203

(looks like with the previous implementation of accessible name, we did exit early in that case)

[kasperisager]

The current behaviour aligns with Firefox and Safari so Chrome seems like the odd one out. Let's keep an eye on w3c/accname#72.

[kasperisager]

I opened w3c/accname#112 to solve this, which may or may not be accepted 🤷

[Jym77]

With the clarification at w3c/html-aam#414 (comment) it seems that empty strings should indeed be rejected and computation goes to next step. Since this is our behaviour, we can close this.