anchor-ambiguous-text: implements check for alt tags on <img /> elements

[mattxwang]

This is a (small) PR that extends getAccessibleChildText to return the alt value of an <img /> (or bound) component instead of traversing its children. As a result, this lets the utility and anchor-ambiguous-text handle anchors that have images as children.

I add a few test cases and update the docs.

Part of (but does not close) #879.

[codecov]

Codecov Report

Merging #880 (bb84abc) into main (c9687cc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #880   +/-   ##
=======================================
  Coverage   99.29%   99.29%           
=======================================
  Files         101      101           
  Lines        1553     1555    +2     
  Branches      510      511    +1     
=======================================
+ Hits         1542     1544    +2     
  Misses         11       11           

Impacted Files	Coverage Δ
src/util/getAccessibleChildText.js	100.00% <100.00%> (ø)

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[ljharb]

Looks good. I'm a bit nervous this will break someone, and it would then need to be reverted and put behind an option, but we can give it a shot.

[mattxwang]

I'm a bit nervous this will break someone, and it would then need to be reverted and put behind an option, but we can give it a shot.

anchor-ambiguous-text wasn't released yet, right? In that case, this would be the "default" behaviour. I also (personally) don't anticipate many use-cases where people have a good reason to have <img alt="click here" /> or something of the sort.

[ljharb]

aha, good point :-) yay!