[Canvas][A11y] Adds an H1 tag with the workpad title when viewing workpads

[cqliu1]

Summary

Related to #61870.
Closes #25494.

This adds an H1 tag with the workpad title for screen readers only and focuses on the title when navigating to this workpad editor page.

I also noticed some strange behavior when you delete your workpad title with the document title and the breadcrumbs, so I made both fallback to displaying the workpad ID when the title is an empty string.

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

Risk Matrix

Delete this section if it is not applicable to this PR.

Before closing this PR, invite QA, stakeholders, and other developers to identify risks that should be tested prior to the change/feature release.

When forming the risk matrix, consider some of the following examples and how they may potentially impact the change:

Risk	Probability	Severity	Mitigation/Notes
Multiple Spaces—unexpected behavior in non-default Kibana Space.	Low	High	Integration tests will verify that all features are still supported in non-default Kibana Space and when user switches between spaces.
Multiple nodes—Elasticsearch polling might have race conditions when multiple Kibana nodes are polling for the same tasks.	High	Low	Tasks are idempotent, so executing them multiple times will not result in logical error, but will degrade performance. To test for this case we add plenty of unit tests around this logic and document manual testing procedure.
Code should gracefully handle cases when feature X or plugin Y are disabled.	Medium	High	Unit tests will verify that any feature flag or plugin combination still results in our service operational.
See more potential risk examples

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[elasticmachine]

Pinging @elastic/kibana-accessibility (Project:Accessibility)

[Heenawter]

Tested locally with screen reader on and off. Ensured that the h1 tag updated as the title was changed, and verified that the focus() on mount impacted behaviour as expected.

Left one simple clarifying question and another about confirming whether or not focusing on the h1 tag is the right move from an a11y stand point, but otherwise, works great 👍

[cqliu1]

@elasticmachine merge upstream

[Heenawter]

The changes look good to me - briefly tested plus code review 👍 Left one tiny nit but otherwise looks great

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 8f31b89
• Storybooks Preview

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
canvas	1.0MB	1.0MB	+446.0B

History

• 💚 Build #58927 succeeded e4ebae3
• 💔 Build #58912 failed aa8c151
• 💚 Build #58457 succeeded 1cb1e4e
• 💔 Build #58405 failed 1ffe29c
• 💔 Build #58378 failed 9728ff1
• 💔 Build #58364 failed 5e050ec

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream