fix(accordion): add heading role and aria level to title

[mivaylo]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• If applicable, have a visual design approval

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Accordion and Stepper headers don't have role and aria-level assigned.

Issue Number: CDE-2437

What is the new behavior?

Accordion and Stepper headers have role=heading and aria-level can be assigned from the user wit hdefaul value of 3.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[github-actions]

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[dtsanevmw]

Check the implementation of stack-view where we are checking if the component is nested so we put 4 instead of 3 for the default value

[kevinbuhmann]

This is a breaking change because it can cause pages with legal heading structure to suddenly have illegal heading structure due to the new headings.

This can be fixed by not setting accordion titles as heading by default to maintain current heading structures. This should be an opt-in feature until v19.

I have added the breaking change label due to the current implementation. If this issue is fixed, that can be removed.