build: fix build under mono msbuild

[kallisti5]

• Correct System.XML reference to System.Xml
• Drop legacy CodeAnalysisRuleSet (recommended per microsoft)
  https://docs.microsoft.com/en-us/visualstudio/code-quality/migrate-from-legacy-analysis-to-net-analyzers
• Fix case of MyPictureBox.Designer.cs

[kallisti5]

This fixes the build of LaserGRBL via msbuild under Linux...

Build succeeded.

"/home/kallisti5/Code/LaserGRBL/LaserGRBL.sln" (default target) (1) ->
"/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj" (default target) (2) ->
(CoreCompile target) -> 
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/WiFiDiscovery/IPAddressHelper.cs(198,27): warning CS0168: The variable 'ex' is declared but never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/WiFiDiscovery/IPAddressHelper.cs(265,8): warning CS0219: The variable 'count' is assigned but its value is never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/Telegram.cs(59,21): warning CS0168: The variable 'ex' is declared but never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/PSHelper/PSEditorForm.cs(89,21): warning CS0168: The variable 'ex' is declared but never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/SvgConverter/ConvertSizeAndOptionForm.cs(87,11): warning CS0219: The variable 'LaserOff' is assigned but its value is never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]
  /home/kallisti5/Code/LaserGRBL/LaserGRBL/RasterConverter/RasterToLaserForm.cs(731,36): warning CS0168: The variable 'ex' is declared but never used [/home/kallisti5/Code/LaserGRBL/LaserGRBL/LaserGRBL.csproj]

    6 Warning(s)
    0 Error(s)

Time Elapsed 00:00:04.82

I'm a bit confused why msbuild creates an exe for Windows from Linux... but the resulting exe works in wine. Running under mono shows the same crash the windows one does.

$ file /home/kallisti5/Code/LaserGRBL/LaserGRBL/bin/Debug/LaserGRBL.exe
/home/kallisti5/Code/LaserGRBL/LaserGRBL/bin/Debug/LaserGRBL.exe: PE32 executable (GUI) Intel 80386 Mono/.Net assembly, for MS Windows

[kallisti5]

Oh, this one is working towards #1867

[kallisti5]

I should mention that the timer issue mentioned in #5 is still present under Mono. Why was 5 closed? Seems like a legitimate bug.

[kallisti5]

Updated for latest code, the mono build now works under Linux creating Windows executables.

[kallisti5]

@arkypita this one should be in a good place to move the needle towards Linux support.

The paid LightBurn software just removed Linux support, so there is going to be a big influx of potential users looking for a laser software with Linux support.