Updated to .net 5

[majastrz]

• Updated to .net 5
• Removed hard-coded .net version in build.yml. It should not fallback to global.json.
• Left core libraries targeting netstandard 2.1
• Upgraded some of the nugets that easily upgraded. The web assembly nugets didn't want to upgrade because of the previous line. We will need to investigate.
• Did not touch any self-contained file settings yet. We can experiment once this goes in.
• Enabled IncludeNativeLibrariesForSelfExtract so we truly get single files for bicep cli instead of the executable plus native libraries.

Testing done on merge validation build artifacts:

• Validated cli on wsl2 and windows (machine without .net 5 installed). Bicep build command worked.
• Validated windows setup (machine without .net 5 installed). Bicep build command worked.
• Installed extension from VSIX in VS code. Runtime was acquired successfully and language server was functional.
• Validated playground locally.

This closes #873.

[majastrz]

I have to update types first and then pull in the new submodule. Then build should pass.

[codecov-io]

Codecov Report

Merging #911 (c3314c9) into main (800d4a8) will decrease coverage by 0.17%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main     #911      +/-   ##
==========================================
- Coverage   94.73%   94.55%   -0.18%     
==========================================
  Files         302      302              
  Lines       13724    13682      -42     
  Branches       12       12              
==========================================
- Hits        13001    12937      -64     
- Misses        723      745      +22     

Flag	Coverage Δ
dotnet	95.20% <100.00%> (-0.18%)	⬇️
typescript	25.78% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/vscode-bicep/src/language/client.ts	0.00% <0.00%> (ø)
src/Bicep.Core.UnitTests/Utils/FileHelper.cs	92.00% <100.00%> (ø)
...ngServer.UnitTests/BicepCompletionProviderTests.cs	100.00% <100.00%> (ø)
....UnitTests/Completions/SymbolKindTestExtensions.cs	72.72% <0.00%> (-27.28%)	⬇️
src/Bicep.Cli/Logging/BicepDiagnosticLogger.cs	81.25% <0.00%> (-18.75%)	⬇️
...icep.LangServer/Extensions/DiagnosticExtensions.cs	85.71% <0.00%> (-14.29%)	⬇️
src/Bicep.Cli/Logging/BicepConsoleLogger.cs	65.38% <0.00%> (-12.40%)	⬇️
src/Bicep.Core/Syntax/ObjectPropertySyntax.cs	95.00% <0.00%> (-5.00%)	⬇️
.../Bicep.Core/TypeSystem/Az/AzResourceTypeFactory.cs	92.30% <0.00%> (-4.62%)	⬇️
src/Bicep.Core/SemanticModel/SymbolValidator.cs	75.00% <0.00%> (-4.17%)	⬇️
... and 24 more