Unit Conversion Inconsistency Between Types

[GabrielKS]

Another sub-issue of #1134 but this one is distinct enough to get its own issue: certain fields are units system-dependent in some structs but not in others. For instance, the result of get_active_power is units system-dependent in ThermalStandard:

PowerSystems.jl/src/models/generated/ThermalStandard.jl

Line 147 in 71b9bf4

get_active_power(value::ThermalStandard) = get_value(value, value.active_power)

but not in Source:

PowerSystems.jl/src/models/generated/Source.jl

Line 105 in 71b9bf4

get_active_power(value::Source) = value.active_power

making it frustrating to try to write polymorphic code that does the right thing for both.

As an incremental fix before the #1134 overhaul, I propose we work towards the principle that each getter function (a) either performs conversion for all types or does not perform conversion for any types and (b) clearly states which of these it is in its docstrings.

[jd-lara]

This has a fix by defining correct getter in the JSON template.

[GabrielKS]

Update from synchronous discussion: there is a nuance here in that Source doesn't have a base power, so it cannot report quantities in device base units. @rodrigomha will add a base power field to Source.

[jd-lara]

@GabrielKS and @rodrigomha did we add base power to the source?