Add / Fix xschem symbols and testbenches for gf180mcu silicon devices.

[StefanSchippers]

Added all the 47 'priority 0' devices in cells/xschem/symbols
Added the 47 testbenches for device ngspice simulation test in cells/xschem/tests
Updated cells/xschem/xschemrc so xschem can be run directly from cells/xschem for testing

Fix order of fields in 'rb' element (resistor body) of Poly resistor models in file models/ngspice/sm141064.ngspice according to ngspice manual:
From:

rb  11 21 ppolyf_u_1k_body l=r_l w=r_w
+r='r_temp*r_n*(r_rsh0+r_vc1*abs(v(11,21))/r_n+r_vc2*abs(v(11,21))*abs(v(11,21))/r_n/r_n)'

to:

 rb  11 21
+r='r_temp*r_n*(r_rsh0+r_vc1*abs(v(11,21))/r_n+r_vc2*abs(v(11,21))*abs(v(11,21))/r_n/r_n)'
+ppolyf_u_1k_body l=r_l w=r_w

Without this change resistor geometry (r_l, r_w) is not taken into account.

[mithro]

Hi @StefanSchippers,

First, thank you for your pull request, it is awesome to see!

There is a current open issue (#1) to update the names of primitives in this repository to match Google's naming standard which is used in the SkyWater PDK (see also https://bit.ly/open-source-pdks-naming).

Do you think we should merge this now or wait for the names to be updated?

Thanks!

Tim '@mithro' Ansell
PS I also logged #7 as we should have some type of CI checking of the xschem files.

[StefanSchippers]

@mithro I can update the device names, however a corresponding change should be done in Ngspice/Xyce model files. If the new xschem device names do not match with their spice models simulation will not work.
Of course a schematic device 'xxx' could link to spice model 'yyy', but I think schematic symbols and spice models should have the same names, otherwise designers experience will be substandard :-).
If this change is to be done it is better to merge in the xschem stuff after the change is completed. Otherwise someone will be using the schematic symbols and complain later when everything has been changed.
PS1: is there someone in charge to do the spice models renaming?
PS2: What is CI ? It's probably Continuous Integration, what does this mean for xschem files (which btw are plain ascii files)? What kind of requirements should I expect from these CI tests?
PS3: If we decide to merge in stuff later, should this pull request be deleted?

Thank you!
Stefan