Change: Decouple and remove landscape-dependent cargo types. (#11719)

Cargo types of default engines, industries and houses are now specified in terms of label.

Feature: NewGRF properties to set town production effect and multiplier. (#11947)

Town production effect is modelled on town acceptance (growth) effect, and so takes an original cargo slot for behaviour instead of a direct value.

NewGRF feature 0x0B, property 0x1E, takes 1 byte.

Valid values are:
- 0x00 to behave like passengers
- 0x02 to behave like mail
- 0xFF to behave like other cargo (i.e. not produced.)

If not set, town production effect is set based on the cargo label ('PASS' or 'MAIL').

Town production multiplier allows adjusting the amount of cargo produces when Town Production Effect is set, without needing to use callbacks.

NewGRF feature 0x0B (cargo), property 0x1F, accepts a 2 byte (word) value, similar to the cargo capacity multiplier property. The default value is 256 which means 100%, i.e. normal rate.

Codechange: Rename TownEffect to TownAcceptanceEffect.

This makes it clearer that TownEffect only affects acceptance behaviour.

Codechange: Rename INVALID_CARGO to INVALID_CARGO_BITNUM

... to avoid future ambiguity.

Codechange: Remove CargoSpec::multipliertowngrowth which is unused (#9701)

This is set by cargo property 19.
This property is only implemented in TTDPatch.