Remove Ply and update to FSharp 6 #812

Job	Run time
build-devcontainer	9m 8s
fable-npm-build (ubuntu-latest, 18)	1m 59s
dotnet-build (Debug, ubuntu-latest)	3m 8s
fable-npm-build (ubuntu-latest, 20)	2m 1s
fable-python-build (ubuntu-latest, 3.10)	2m 50s
dotnet-build (Debug, windows-latest)	5m 29s
fable-npm-build (ubuntu-latest, latest)	2m 1s
fable-python-build (ubuntu-latest, 3.11)	2m 58s
dotnet-build (Debug, macOS-latest)	6m 25s
fable-npm-build (windows-latest, 18)	5m 57s
fable-python-build (ubuntu-latest, 3.12)	3m 3s
dotnet-build (Release, ubuntu-latest)	3m 5s
fable-npm-build (windows-latest, 20)	5m 55s
fable-python-build (windows-latest, 3.10)	7m 1s
dotnet-build (Release, windows-latest)	4m 53s
fable-npm-build (windows-latest, latest)	6m 28s
fable-python-build (windows-latest, 3.11)	5m 21s
dotnet-build (Release, macOS-latest)	3m 46s
fable-npm-build (macOS-latest, 18)	3m 2s
fable-python-build (windows-latest, 3.12)	5m 49s
fable-npm-build (macOS-latest, 20)	3m 14s
fable-python-build (macOS-latest, 3.10)	4m 11s
fable-npm-build (macOS-latest, latest)	4m 7s
fable-python-build (macOS-latest, 3.11)	5m 14s
fable-python-build (macOS-latest, 3.12)	5m 18s
	1h 52m 23s

Provide feedback