Add TI DACx0504 family

I added the DACx0504 family of Texas Instruments quad output DACs. Analogous to the existing DACx0502 symbols, DAC80504 is the parent symbol, DAC70504 and DAC60504 are derived from it.

• Datasheets (they all link to SBAS871C):
  • https://www.ti.com/lit/gpn/dac80504
  • https://www.ti.com/lit/gpn/dac70504
  • https://www.ti.com/lit/gpn/dac60504
• Footprint
  • There is a merge request for the matching footprint: kicad-footprints!3641 (merged)
  • There is a merge request for the matching footprint generator script: kicad-footprint-generator!1126 (merged)

• I did not stack Pins 6 and 17 for two reasons:
  1. According to the datasheet "The thermal pad should be connected to any internal PCB ground plane" (p. 5), but not "must be"
  2. Leave the choice of split vs. combinded digital/analog GND planes to the circuit designer
• The default footprint is set to Texas_RTE0016D_WQFN-16-1EP_3x3mm_P0.5mm_EP0.8x0.8mm_ThermalVias, because the datasheet specifies: "The thermal pad should be connected to any internal PCB ground plane using multiple vias for good thermal performance." (p. 5)