Keep information about '+' and '-' in PMG weight names
In a previous MR !67266 (merged), @jolamber had noticed that downstream analysis code can run into issues when passed generator-level weight names that contain the symbols '+' or '-'. This was in the context of scale variations, where the factors of 0.5 and 2.0 are easily understood, so the signs were simply removed (mapped to a blank string).
We are now considering weights where we do need to keep the information about '+' and '-', and therefore propose to change the behaviour of the PMG utils to rename those to 'plus' and 'minus' instead of a blank string.