fix: accname related role edge cases

[jlp-craigmorten]

Changes

Relates to #25

• img element mappings now prefer image role over img, see the note in https://www.w3.org/TR/html-aam-1.0/#el-img r.e. preferred synonym for WAI-ARIA 1.3
• img element with no alt attribute (i.e. missing completely) has a role of image, see https://www.w3.org/TR/html-aam-1.0/#el-img
• img element with empty alt has a role of none provided the img does not have an accname provided by other means (e.g. aria-label), see https://www.w3.org/TR/html-aam-1.0/#el-img-empty-alt
• aria-label should be trimmed of whitespace when calculating accname, see https://www.w3.org/TR/accname-1.2/#computation-steps (specifically section 2.4 of the algorithm)
• title should be considered when calculating accname, see https://www.w3.org/TR/accname-1.2/#computation-steps (specifically section 2.5 of the algorithm) for the core calculation and see https://www.w3.org/TR/html-aam-1.0/#el-img-name for the img specific name calculation

How to Review

This change was prompted by the following failing test cases taken from the WPT roles-contextual.html suite:

• el-aside-in-section-aria-label-whitespace
• el-aside-in-section-aria-labelledby-empty
• el-aside-in-section-aria-labelledby-whitespace
• el-aside-in-section-title
• el-img-empty-alt-aria-label-whitespace
• el-img-empty-alt-aria-labelledby-empty
• el-img-empty-alt-aria-labelledby-whitespace
• el-img-no-name
• el-section-aria-label-whitespace
• el-section-aria-labelledby-non-existing
• el-section-aria-labelledby-empty
• el-section-aria-labelledby-whitespace
• el-section-title

This change does not cover the following known failures:

• el-aside-in-section-aria-labelledby-non-existing
• el-img-empty-alt-aria-labelledby-non-existing
• el-th-in-row (from the WPT table-roles.html suite)

These would require a more accurate ACCNAME algorithm implementation for the first two, and supporting an involved algorithm to scan all rows in a table to support rowheader when scope is auto.

Checklist

• Unit tests updated

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🦋 Changeset detected

Latest commit: 297c359

The changes in this PR will be included in the next version bump.

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[drwpow]

Amazing! Thank you!