Promote experimentalToolbar out of experimental

[blakewilson]

Similar to taking the plugin system out of experimental, let's take the toolbar out of experimental as well.

We should still support the experimentalToolbar property in the config, but if used, console a warning that they should be using toolbar instead and that experimentalToolbar will be removed in the next major release.

Take a look at the PR for taking the plugin system out of experimental for inspiration:
#1807

Acceptance Criteria

• Deprecate shouldShowFaustToolbar property and log a warning when encountered, tell user to use shouldShowAdminToolbar which is controlled by the wp-admin setting on the user's profile.
• Use shouldShowAdminToolbar property to control Toolbar rendering
• Be mindful of bundle size increase when including Toolbar
• Write new issue to remove backwards compatibility in next major semver release

If we determine that enabling this by default causes an unacceptable performance hit, we will disable it by default until a later time.