Require denomination pricing for price and price_postapoc

[RenechCDDA]

Summary

Infrastructure "Item price and price_postapoc must be denominated (cents/USD/kUSD). Integer values no longer used"

Purpose of change

#78901 (comments)

Describe the solution

Throw error if an integer is found

Print list of valid denominations, so that the cent/cents conundrum is clearly communicated to our contributors . Pulls directly from money_units, so should be future proofed.

Also the following units are now accepted as subsitutes:
cents--->cent
dollar--->USD
dollars--->USD

Describe alternatives you've considered

Also accept cents as a valid unit which converts to 1_cent. Single line change in units.h, but not sure if it's a good idea doing that.

Testing

Additional context

In draft until I do all the JSON stuff

[RenechCDDA]

Ooooooooooh okay, I don't think we can do the aliasing without some really nasty stuff.

So if both "cent" and "cents" are valid, it reads cent and assumes the unit will be "cent". Then it throws an error, because the value it ends up reading is "cents", which is one character too many! The program can read, .e.g. 2 dollar 40 cent. It does this by finishing reading the 2 dollar portion, then reading the next character to see if there is anything else.

If our input is instead 2 dollars 40 cents (notice the dollars, plural) then it encounters an s. It expected to read either a space(which it would skip) or another number value (the 40 cent) which it would add to the existing value. But it found an s instead, so it doesn't know what to do.

We could maybe, maybe, change the order of units in units::money so that dollars is before dollar and cents is before cent, so that it always reads the longer one first. But that seems nasty!