Add support for parameters, equations... for @connectors

[ven-k]

• @connector now supports @parameters, @equations, @extend, @variables, @components and a begin...end block along with variables specified without a begin block.
• This is useful for connectors like HydraulicFluid¹
• Replaces internal functions connect_macro and mtkmodel_macro with _model_macro, which handles both based on the isconnector flag
• Adds "Connector with parameters, equations..." for testing the enhancement.

Footnotes

1. https://github.com/SciML/ModelingToolkitStandardLibrary.jl/blob/main/src/Hydraulic/IsothermalCompressible/utils.jl#L53-L75 ↩

[ven-k]

Additionally, generated function <Model>.f will have an identifiable name __<Model>__. This will make it easier to identify the components in the stack trace.

julia> @mtkmodel A begin
       end
ModelingToolkit.Model{typeof(__A__), Dict{Symbol, Any}}(__A__, Dict{Symbol, Any}(:kwargs => Dict{Symbol, Any}(), :independent_variable => t), false)

julia> A.f
__A__ (generic function with 1 method)