Use initialOptions to save & restore view state on navigation

[MetRonnie]

Secondary PR against cylc#1664

The view state (filters, inputs, toggles etc.) can now be saved with the Lumino tab layout by using a prop called initialOptions.

This is only implemented for the log view for now.

[MetRonnie]

Rejigged the watchers for file and id to prevent race conditions. The usual order of events now is (for the example of opening the workflow log):

1. id gets set for the first time to '~user/workflow'. file is nullish.

   • updateQuery() gets called because the id changed, but because file is nullish it doesn't really do anything

     cylc-ui/src/views/Log.vue

     Lines 429 to 431 in 58f5d96

     	if (!this.file || !this.id) {
     	this.query = null
     	return

   • updateLogFileList() gets called because the id changed

2. file has been set to the default scheduler log by updateLogFileList()

   • updateQuery() gets called again because file changed, and causes the log file to display
   • updateLogFileList() doesn't get called because id is unchanged

[MetRonnie]

x in arr does not do what you think it does!

[MetRonnie]

This is similar to using a writeable computed property e.g.

computed({
  get: () => props.initialOptions[name],
  set: (val) => emit(
    updateInitialOptionsEvent,
    { ...props.initialOptions, [name]: val }
  )
})

but that seemed to lead to the ref value not updating until the next tick? Maybe the watcher approach works because it is backed up by a concrete ref? Not sure

[MetRonnie]

Re-opened as cylc#1688