Diode_SMD: improve silkscreen clearance (fix invisible cathode markings)

I was assembling a PCB that was created in KiCad today and noticed that the line marking the cathode on all the diodes is invisible because there isn't enough clearance between it and the pads. I searched the open issues here and found #1425 (closed), which links to a forum post that reported this. That post shows what it looks like from within KiCad itself, but i've attached a photo of my real-world board (produced by JLCPCB in Dec 2022) in case that's helpful too

Although the forum post and my board only demonstrate the problem with SOD-123s, it seems to affect many of the SMD diode footprints in the official library. I determined this based on the fact that (like SOD-123) they only have about 0.09 mm clearance between pad and silkscreen — the library conventions (F5.1) suggest 0.2 mm. This PR updates all of them to match that recommendation

In a few cases, the upper and lower parts of the outline weren't quite 0.2 mm away from the pads either, so i changed those as well. In some of those cases, moving the lines caused them to touch or overlap the reference designator, so i also moved that farther away. There doesn't seem to be an official recommendation as to how far away reference designators should be from courtyard or silkscreen lines, and it varies a lot in the existing footprints, but it seemed like roughly 0.8 to 0.9 mm is common so i standardised on that

I also adjusted the reference designator for SOD-128, which technically wasn't touching the silkscreen outline but was much closer to it than the others (and was inside the courtyard)

I've attached an example before/after to demonstrate the type of changes made

PS: #1425 (closed) suggests that these footprints 'might be best scripted'. I double-checked the current kicad-footprint-generator repository to see if that was ever followed up on, but the directory for SMD diodes contains only a reference to a file that doesn't exist, and grepping for e.g. 'SOD-123' doesn't return any results, so i take that to mean that these are still manually updated. If that's not the case, please let me know where else i should fix them