Refactor Test Application

[Westbrook]

Code of conduct

• I agree to follow this project's code of conduct.

Description of issue

Tests have been added to the project in a fairly ad hoc manner throughout its history. Refactoring tests to be delivered in via the following follows would make for component to component consistency and for a more clear destination for additional test contexts over time:

• declarative.test.ts: test all declarative usage of the element in question
• imperative.test.ts: all imperative interactions
• keyboard.test.ts: all keyboard interactions
• a11y-tree.test.ts: the delivered a11y tree across various states
• controlled.test.ts: that the element can be "controlled" by the parent application
• etc.

To Dos:

• accordion
• action-bar
• action-button
• action-group
• action-menu
• alert-dialog
• asset
• avatar
• badge
• banner
• button
• button-group
• card
• checkbox
• clear-button
• close-button
• coachmark
• color-area
• color-field
• color-handle
• color-loupe
• color-slider
• color-wheel
• combobox
• dialog
• divider
• dropzone
• field-group
• field-label
• help-text
• icon
• icons
• icons-ui
• icons-workflow
• iconset
• illustrated-message
• infield-button
• link
• menu
• meter
• modal
• number-field
• opacity-checkerboard
• overlay
• picker
• picker-button
• popover
• progress-bar
• progress-circle
• quick-actions
• radio
• search
• sidenav
• slider
• split-button
• split-view
• status-light
• swatch
• switch
• table
• tabs
• tags
• textfield
• thumbnail
• toast
• tooltip
• top-nav
• tray
• underlay
• base
• bundle
• grid
• opacity-checkerboard
• reactive-controllers
• shared
• styles
• theme
• truncated

[najikahalsema]

The meat of this work will be addign tests to the controlled test group.

[nikkimk]

Instead of a11y-tree.testing.ts being separated into its own file, a11y tree testing should be a part of all of the other test files.