[Maintenance] Remove undefined prop defaults

[LarryHu0217]

Closes #8352

Describe your changes:

Remove explicit default: undefined entries from optional non-Boolean Vue props now that vue/require-default-prop is disabled. Those props still resolve to undefined when omitted.

Also remove the unused isHeaderTitle Boolean prop from TableColumnHeader.vue. Vue casts an omitted Boolean prop without an explicit default to false, so removing this dead prop avoids introducing that runtime semantic change.

Testing:

• Prettier check on all 12 changed Vue files
• ESLint on all 12 changed Vue files
• Vue 3.4 SSR runtime matrix for omitted Boolean, String, Number, Object, and Array props
• rg -n "default:\\s*undefined|default\\s*\\(\\)\\s*\\{\\s*return\\s+undefined|default:\\s*void\\s+0" src example e2e returned no matches
• npm run build
• npm test — 975 passed, 67 skipped
• git diff --check

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Is this a notable change that will require a special callout in the release notes? No, this is a maintenance cleanup only.

Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes? No new repository tests; the direct Vue runtime matrix and full existing suite cover the behavior.
• Has this been smoke tested?
• Have you associated this PR with a type: label? Maintainer permissions are required.
• Have you associated a milestone with this PR? Left for maintainers.
• Testing instructions included in associated issue OR is this a dependency/testcase change?

Reviewer Checklist

• Changes appear to address issue?
• Reviewer has tested changes by following the provided instructions?
• Changes appear not to be breaking changes?
• Appropriate automated tests included?
• Code style and in-line documentation are appropriate?