fix(alert): correctly position alert when keyboard is open

[liamdebeasi]

TODO: Give co-author credit when merging

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?

Issue Number: #17776
The alert was not inheriting the height of ion-app because it had position: fixed. As a result, it was still being sized/positioned relative to the viewport.

What is the new behavior?

• Changing to position: absolute now causes ion-alert to inherit the height from ion-app

Does this introduce a breaking change?

• Yes
• No

Other information