Add resample method option for "set DPI" action

[fireattack]

Currently, if you use "set DPI" action and choose "keep print size", which will resize the image, there is no way to choose resample method.

From what I observed, the resample method is worse than what you can achieve with Lanczos method in "resize" action.

Currently, if I want to, say, resize 600dpi to 300dpi (keep print size, so resized to 50%), I have to use two actions, one "resize" for actual resizing, and then another "set DPI" purely for changing the metadata. This is kinda tedious especially if your target DPI changes (you need to re-calculate the percentage manually from your original DPI to whatever new DPI you want.)

(This is a general suggestion for all the products that with conversions.)