Clean up Blockly UI Events

[moniika]

Is your feature request related to a problem? Please describe.

UI events in Blockly don’t fit the Blockly.Events.Ui pattern well.

• properties for events don’t fit the names element, newValue, and oldValue well
• properties of Ui events cannot be typed well (for newValue and oldValue)
• for some events, oldValue doesn’t add any information (like in mutatorOpen, warningOpen, commentOpen)
• some newer UI events, like viewport change, have multiple “new” properties (viewport coordinates and scale)

Describe the solution you'd like

Split ui events into different events, setting the type based on logical grouping and building in some other way to distinguish these events as ui events.
These events could inherit from a UI events interface and have a property isUiEvent=true and have AbstractEvent first declare this property (false by default, but true for ui events)

Current UI Events and properties:

element	oldValue	newValue
dragStart	null	this.draggingBlock_.getDescendants(false)
dragStop	this.draggingBlock_.getDescendants(false)	null
selected	null or id	null or id
click	null	'workspace' or 'block'
cursorMove	oldNode	newNode
markerMove	oldNode	newNode
commentOpen	true or false	true or false
mutatorOpen	true or false	true or false
warningOpen	true or false	true or false
trashcanOpen	true or false	true or false
category	old category name or null	new category name or null
theme	null	null

New grouping of events and properties:

class	type	properties	old ui events
Blockly.Events.BlockDrag	drag	blocks, isStart	dragStart, dragStop
Blockly.Events.Selected	selected	oldElementId, newElementId	select
Blockly.Events.Click	click	targetType	click
Blockly.Events.MarkerMove	marker_move	oldNode, newNode, isCursor	cursorMove, markerMove
Blockly.Events.BubbleOpen	bubble_open	isOpen, bubbleType	commentOpen, mutatorOpen, warningOpen
Blockly.Events.TrashcanOpen	trashcanOpen	isOpen	trashcanOpen
Blockly.Events.ToolboxItemSelect	toolbox_item_select	oldItem, newItem	category
Blockly.Events.ThemeChange	theme_change	themeName	theme
Blockly.Events.ViewportChange	viewport_change	viewTop, viewLeft, scale	zoom

Describe alternatives you've considered

Split into different events, while still sharing the same (‘ui’) type and adding a sub-type to further distinguish the type of event. This, however, wouldn't work well with registering events and serialization/deserialization since the type is what is used for registration (and deserialization) and we can’t register multiple events with the same type.

Additional context

Viewport event #1052