Infrastructure: Add Prettier ESLint config

[nschonni]

Related to #1180
Kept the the defaults, except for the quoting, that seems primarily single quotes

[github-actions]

Examples without any regression tests:

button/button_idl.html
dialog-modal/alertdialog.html


Examples missing some regression tests:

combobox/combobox-autocomplete-both.html:
    combobox-id
combobox/combobox-autocomplete-list.html:
    combobox-id
combobox/combobox-autocomplete-none.html:
    combobox-id
combobox/grid-combo.html:
    textbox-key-down-arrow
    textbox-key-up-arrow
dialog-modal/datepicker-dialog.html:
    textbox-aria-describedby
menu-button/menu-button-actions-active-descendant.html:
    menu-up-arrow
    menu-down-arrow
    menu-character
spinbutton/datepicker-spinbuttons.html:
    spinbutton-down-arrow
    spinbutton-up-arrow
    spinbutton-page-down
    spinbutton-page-up
    spinbutton-home
    spinbutton-end
toolbar/toolbar.html:
    toolbar-tab
    toolbar-right-arrow
    toolbar-left-arrow
    toolbar-home
    toolbar-end
    toolbar-toggle-esc
    toolbar-toggle-enter-or-space
    toolbar-radio-enter-or-space
    toolbar-radio-down-arrow
    toolbar-radio-up-arrow
    toolbar-button-enter-or-space
    toolbar-menubutton-enter-or-space-or-down-or-up
    toolbar-menu-enter-or-space
    toolbar-menu-down-arrow
    toolbar-menu-up-arrow
    toolbar-menu-escape
    toolbar-spinbutton-down-arrow
    toolbar-spinbutton-up-arrow
    toolbar-spinbutton-page-down
    toolbar-spinbutton-page-up
    toolbar-checkbox-space
    toolbar-link-enter-or-space
    toolbar-aria-controls
    toolbar-button-aria-pressed
    toolbar-button-aria-hidden
    toolbar-radiogroup-role
    toolbar-radiogroup-aria-label
    toolbar-radio-role
    toolbar-radio-aria-checked
    toolbar-radio-aria-hidden
    toolbar-button-aria-disabled
    toolbar-menubutton-aria-label
    toolbar-menubutton-aria-haspopup
    toolbar-menubutton-aria-controls
    toolbar-menubutton-aria-expanded
    toolbar-menu-role
    toolbar-menu-aria-label
    toolbar-menuitemradio-role
    toolbar-menuitemradio-aria-checked
    toolbar-menuitemradio-tabindex
    toolbar-spinbutton-role
    toolbar-spinbutton-aria-label
    toolbar-spinbutton-aria-valuenow
    toolbar-spinbutton-aria-valuetext
    toolbar-spinbutton-aria-valuemin
    toolbar-spinbutton-aria-valuemax


Examples documentation table rows without data-test-ids:

dialog-modal/alertdialog.html
    "Keyboard Support" table(s):
       Tab
       Shift + Tab
       Escape
       Command + S
       Control + S
    "Attributes" table(s):
       alertdialog
       aria-labelledby=IDREF
       aria-describedby=IDREF
       aria-modal=true
       alert

SUMMARTY:

  55 example pages found.
  2 example pages have no regression tests.
  8 example pages are missing approximately 61 out of approximately 775 tests.

ERROR - missing tests:

  Please write missing tests for this report to pass.

[nschonni]

This seemed to be the more common pattern so I used this over the default double quote

[spectranaut]

This looks great too!

After this merges @jongund, npm run lint:es will fail on a lot more things related to coding style -- but you can fix all of these failures by running npm run fix. It will break long lines up into multiple lines and switch double quotes with single quotes and other things like this. You will probably have to run npm run fix on all your open PRs once this merges.