Clean up Blockly BlockChange Events

[BeksOmega]

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

Similar to #4203

The BlockChange event type covers lots of different kinds of changes, when ideally it would be split up into more even types. Encapsulating them in a single type causes problems with:

• Undo and redo. Currently this has to be handled using a switch statement.
• Adding new types of change events. See Change event element registry #3793
• Firing new events. For example, because the new and old values must be explicitly passed to the event, anywhere firing an event must duplicate logic to access those values, or create a helper function. See fix: insertion markers and change events to work with JSO hooks #5378

Describe the solution you'd like

Split the BlockChange event into different events.

Current setup:

element	old value	new value	field
field	any	any	string
comment	string	string	null
collapsed	boolean	boolean	null
disabled	boolean	boolean	null
inline	boolean	boolean	null
mutation	string	string	null

Suggested classes:

class	properties
BlockFieldChange	oldValue, newValue, fieldName
BlockCommentChange	oldComment, newComment
BlockCollapsedChange	isCollapsed
BlockDisabledChange	isDisabled
BlockInlinedChange	isInline
BlockMutationChange	oldMutation, newMutation, isXml