Re-export Spectrum ButtonGroup and make dh Button compatible

[bmingles]

We want to re-export Spectrum's ButtonGroup from @deephaven/components, however, We are not planning to re-export Spectrum's Button, so we need to make it compatible with Spectrum's ButtonGroup

• Apply Spectrum styling to DH Button via useSlotProps hook
• Re-export Spectrum ButtonGroup

e.g. We should be able to add something like this to our Button component.

const { UNSAFE_className } = useSlotProps<{ UNSAFE_className?: string }>(
  {},
  'button'
);

...
<button
  ...
  className={classNames(
     ...
     className,
     UNSAFE_className
  )}