The message allows per-wiki configuration. The default target is better
for normal users of TemplateData than the previous hard-coded one and
has already been translated in some languages from when it was used
previously.
This also moves the messages dependencies from `ext.templateData` to
`ext.templateDataGenerator.ui`, which is the only module that uses
them: the correct strings were displayed only by inheritance.
Bug: T112011
Change-Id: I81ab684bb0ed9b0767df75635284c51129ac7000
Add a sourceHandler that deals with all source-related actions
like fetching template source and validating the existing
TemplateData string.
Also add a MessageDialog warning the user in case the TemplateData
is invalid. In this case, the user will be given the option either
to correct the JSON by hand or to start the editor to replace the
existing TemplateData with a new one.
Bug: T91730
Bug: T91325
Change-Id: I4e6d04f02565a02d8dcf5c70a575ab6433caa27f
