Ensure consistency between mask operator and probability operator

[daflack]

Something else

To provide a consistent way of entering conditions the mask operator, and associated recipes (such as rain presence) will require updating to be consistent with the probability using lettering for conditions rather than symbols.

The reason for using lettering rather than symbols during the probability PR (#1677) was to allow looping over multiple conditions as the recipes were overwritten during the parbake step if a symbol was used rather than lettering.

[jfrost-mo]

OFFICIAL

the recipes were overwritten during the parbake step if a symbol was used rather than lettering.

This comes from our filename normalisation. All non-alphanumeric (plus `-_`) characters are replaced with `_` in filenames, so they work reliably in URLs and with certain filesystems. Because the recipe filename is taken from the title of the recipe, it ends up being normalised to the same value. I'm not sure what the optimal way around it is however. OFFICIAL

[daflack]

Makes sense, I've done a fix in the linked PR that uses text and alters the documentation and tests accordingly, as feel need to be consistent. Given the text I've used is standard text notation for these I think it is okay to do this. I don't think there will be any situations where we would need to use symbols in file names so don't think we need to think harder into the optimal way around it.