Several components specify defaults instead of guesses

[avinashresearch1]

Describe the bug 🐞
Several components e.g.,

ModelingToolkitStandardLibrary.jl/src/Electrical/utils.jl

Line 35 in 02a134c

@variables begin

ModelingToolkitStandardLibrary.jl/src/Electrical/utils.jl

Line 72 in 02a134c

@variables begin

ModelingToolkitStandardLibrary.jl/src/Electrical/Analog/sensors.jl

Line 152 in 02a134c

@variables begin

ModelingToolkitStandardLibrary.jl/src/Blocks/continuous.jl

Line 548 in 02a134c

@variables x(t)[1:nx]=x [

ModelingToolkitStandardLibrary.jl/src/Blocks/continuous.jl

Line 621 in 02a134c

@variables begin

specify variables with defaults instead of guesses. Specifying a default in MTK v9 would mean that an explicit constraint is added to the initialization problem which often makes the problem infeasible or extremely overdetermined. This would be the equivalent of setting fix = true and specifying a start` value in Modelica.

[avinashresearch1]

#281 fixes for some Thermal and Blocks components.

[avinashresearch1]

Also: should the x passes into FirstOrder be a guess not a default:

ModelingToolkitStandardLibrary.jl/src/Blocks/continuous.jl

Line 119 in 3a8fb0a

@mtkmodel FirstOrder begin

similar for SecondOrder