Nullchecks for visual elements

Arrow UI elements can now be deleted without causing null reference crash.

Faster player list

• The player list now shows one button for each player, and you can scroll vertically if there's lots of players
• Udon Sharp is now required (Udon Graph is great for simple programming! But this project is simply easier to maintain if I don't bother with Graph, so it's all U# going forward)
• Fixed a theoretical issue that could happen if two players tried to click Hide me at the same time (one player would lose the data race and not be hidden)

Improved UI appearance!

Thanks to Luna for swapping UI Text for Text Mesh Pro and giving the UI panel nice new colors and look.

Initial release!

This prefab is a UI panel that lets players scroll through the list of connected players and teleport to one of them. There's also a "Hide me" option that removes you from the list globally.

--- IMPORTANT:
Drag and drop; no configuration required.

I recommend placing a single Find Your Friends panel in a place easily accessible from your world's spawn. That way players can freely respawn to access the panel again and teleport to new people.

--- LESS IMPORTANT:
You can place multiple panels in your world, but I don't recommend that for now, since references won't work as expected. I may add that feature in the future.

Udon Sharp is not required for this prefab. You can safely delete the FindYourFriends_us script and asset. They are provided as a fully equivalent alternative to the default Udon Graph asset.

This prefab is available on github (github.com/jokerispunk) and I'll be accepting pull requests eventually. I'm not an artist and an aesthetic rework of the UI panel would be welcomed.

Thanks to Fairly Sad Panda (github.com/fairlysadpanda) for networking guidance, and thanks always to the VRCPrefabs community (vrcprefabs.com).