chore: refactor KeySelection and ValueSelection

[josdejong]

For reference, see #460, #454

This PR changes:

export interface KeySelection {
  type: SelectionType.key
  path: JSONPath
  edit?: boolean
}

export type ValueSelection = {
  type: SelectionType.value
  path: JSONPath
  edit?: boolean
}

into:

export interface KeySelection {
  type: SelectionType.key
  path: JSONPath
}

export interface EditKeySelection extends KeySelection {
  type: SelectionType.key
  path: JSONPath
  edit: true
  initialValue?: string
}

export type ValueSelection = {
  type: SelectionType.value
  path: JSONPath
}

export interface EditValueSelection extends ValueSelection {
  type: SelectionType.value
  path: JSONPath
  edit: true
  initialValue?: string
}

Breaking changes:

• the types of KeySelection and ValueSelection are changed
• the helper functions createKeySelection and createValueSelection are changed (argument edit is removed), and two new helper functions are added: createEditKeySelection and createEditValueSelection
• the API of the component EditableValue is changed

Motivation:

• Get rid of some internal workarounds to initialize the value of a key or value when starting to edit it: insertActiveElementContents, tick2, refreshEditableDiv, attaching a .refresh() method to the editable div.
• Make the types more explicit (no optional boolean edit), make use of the commonly used helper functions createKeySelection and createValueSelection more compact.