Update `text` functions to `html` to support inserting the `span` elements
Specify `html: false` for various instances where a `span` is not desired, e.g. `placeholder` and `title` attributes
Make context the first argument of operation objects
Add Paste operation to edit menu when opening the context menu on a blank area of the map (close#2508)
Consolidate localization behavior and init to a coreLocalizer function and singleton
Explicitly support `en-US` locale
Rename coreData to coreFileFetcher and export a singleton rather than using a property of coreContext
Add `apiConnections` property of coreContext to simplify adding a source switcher
Replace some init functions with re-callable, promise-supporting `ensureLoaded` functions
Make coreContext itself load the UI if a container has been specified at init time
Fix code tests
Now that addNode tries to preserve circularity, this
could cause the continued segment to loop back.
And anyway it's confusing why one vertex allows it and none others do.
