feat(input, toggle): add escape hatch property

[liamdebeasi]

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)
  • Some docs updates need to be made in the ionic-docs repo, in a separate PR. See the contributing guide for details.
• 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?

There is no escape hatch for Ionic's automatic opt-in behavior for the modern form markup. Since the opt-in logic is not perfect, there may be instances of components that are opted-in when developers are not ready to adopt the new markup.

What is the new behavior?

• Adds a legacy property to both ion-input and ion-toggle. When true, the component will always use the legacy form markup.

A couple notes:

1. This will be removed in an upcoming major release of Ionic.
2. The escape hatch for the remaining form controls will be done in their respective feature PRs.

Does this introduce a breaking change?

• Yes
• No

Other information