RE documentation-lint: It appears they need javadocs then.
(quoting from your description)
These string constants are handled inconsistently in different factories
Can you give an example of how the same parameter is handled differently? AFAICT This patch doesn't address that. Such inconsistencies, if they exist, would be more important to resolve than moving Strings constants to an interface IMO.
I think limiting the scope of this patch to common parameters is well enough. In doing so, they can be documented in one place (please do that). I'm not sure what value/point there is in doing anything more with other parameters (used by one class), or trying to overcome any inter-package complications. So minGramSize etc. could just be defined in the same common one. At least that's my opinion; it's kind of a bike-shed issue of taste.