Customize: Clean up longstanding annoyances in JS API

[westonruter]

There are some annoyances when working with the JS API which aren't present when working with the PHP API. In particular:

• Manually crafting the content param for the <li> container.
• Lack of default params for active=true and priority=10.
• Having to create panels, sections, and controls with an options object that contains a single params key with the actual object that has the options in it. Why not just pass params directly?
• Inability to specify the templateId via param.
• Redundantly having to supply an id in addition to an instance when add'ing a Panel, Control, Notification, or any other such object that is added to Values instances.

This is a subset of #30741.
Initially #28709 and #29572 .

​https://github.com/xwp/wordpress-develop/pull/274

In 41726:

Customize: Improve usability of Customize JS API.

• Eliminate need to pass both ID and instance in calls to Values#add() for panels, sections, controls, settings, partials, and notifications.
• Eliminate need to supply content param when constructing a Control.
• Unwrap the options.params object passed in constructors to just pass a flat options. (Back-compat is maintained.)
• Add support for templateId param for Control to override which template is used for the content.
• Remove unused previewer being supplied in Control instances.
• Rename classes to containerClasses on Notification.
• Automatically supply instanceNumber to improve stable sorting.
• Use api.Notifications for notifications in settings instead of api.Value.

See #30741.
Fixes #42083.

In 41739:

Customize: Fix theme details modal by updating logic in getPreviousTheme and getNextTheme to not rely on DOM traversal and manually constructing control IDs.

Amends [41726].
See #42083, #37661.

In 41750:

Customize: Allow controls to be created with pre-instantiated Setting object(s), or even with plain Value object(s).

• Allow passing settings in keyed object (e.g. settings: { default: 'id' } ), or as an array (e.g. settings: [ 'id' ]) with first being default; again, Setting/Value` objects may be supplied instead of IDs.
• Allow a single setting to be supplied with just a single setting param, either a string or a Setting/Value object.
• Update changeset_status and scheduled_changeset_date to be added dynamically with JS and simply passing of api.state() instances as setting.
• Introduce a data-customize-setting-key-link attribute which, unlike data-customize-setting-link, allows passing the setting key (e.g. default) as opposed to the setting ID.
• Allow WP_Customize_Control::get_link() to return data-customize-setting-key-link when setting is not registered.
• Eliminate default_value from WP_Customize_Date_Time_Control since now comes from supplied Value.
• Export status choices as wp.customize.settings.changeset.statusChoices.
• Export date and time formats as wp.customize.settings.dateFormat and wp.customize.settings.timeFormat respectively.

Props westonruter, sayedwp.
See #39896, #30738, #30741, #42083.
Fixes #37964, #36167.

In 42035:

Customize: Ensure id for section and panel is passed among params to respective templates.

Fixes issue where JS-added Publish Settings section failed to get container element ID set properly to hide its section-meta.

Amends [42025].
See #42337, #42083.

In 42037:

Customize: Support instantiation of partials with flat/unwrapped params for parity with controls, sections, and panels in [41726].

• Passing options.params when constructing Partial is now deprecated in favor of just passing options.
• Improve usage of jsdoc in JS Partial class.
• Also add defaults property to wp.customize.selectiveRefresh.Partial class for parity with Control.

See #42083.

In 42038:

Customize: Fix interface alignment between Setting and Control, adding defaults to wp.customize.Setting and using wp.customize.previewer as default previewer param.

Also move jsdoc from class to initialize method and correct the param types.

Amends [41726], [42037], [32681].
See #42083, #30737.

In 42048:

Customize: Consolidate sourcing of control params.

Prevent needlessly iterating over controlConstructor to find type when it is already supplied.

Amends [41750], [41726].
See #42083.