chore(): create reusable test header

[mapsandapps]

Implemented

There's now a reusable header component that will allow a developer of Ionic Framework to toggle a number of things while viewing the index.html test files. This component can be reused across any of these files and includes:

• Dark mode toggle
• Theme switcher for iOS, MD, and Ionic themes
• LTR/RTL

It also has a slot so that settings can be added, e.g. settings that are specific to the component being tested like the ones we have for some Datetime tests.

Yet to do

1. I wasn't sure where to put the test-header.tsx file nor did I figure out how to prevent it from being included in Ionic Framework.

2. Other functionality we might want to add to the popover:

   • Mode
   • Locale
   • Maybe more?

3. Currently, not all of the options persist when selecting other options. Several of the options are settable via URL query parameters. We may want to update the component to add and remove params accordingly (like it currently does for theme, so they will persist.

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