fix(label): text overflow for slotted headings

[simonhaenisch]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Headings that are put in the slot of an ion-label don't inherit the text-overflow: ellipsis style.

Issue Number: #17087.

What is the new behavior?

• Adds styling for slotted headings to inherit overflow and text-overflow.

Does this introduce a breaking change?

• Yes
• No

If anyone really wanted headings inside labels to just have hidden overflow (very unlikely), they'd need to explicitly set the overflow.

Other information

Closes #17087.

master	branch

[brandyscarney]

This looks good! Thank you! I made a small change to the test just to reduce the amount of words so that it would all fit in the screenshot. 🙂