447854: Switch computation of an IFormField's enclosing field path to
new template detection

Change-Id: I23369865026b1eb553ded8cbaec50ca37e691e6e
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=447854
Reviewed-on: https://git.eclipse.org/r/35132
Tested-by: Hudson CI
Reviewed-by: Andi Bur <andi.bur@gmail.com>