Add | Add net8 compatibility

[Wraith2]

closes #1930

In netcore builds SqlGuidCaster and the type workaround that used it are not required. The problem they solved has already been change to use the ReadOnlySpan ctor. The SqlGuid workarounds in netcore are removed. Netfx builds use a more recent approach to the original problem and do not need to change.

I have also added ifdeffed use of the new api's introduced to the ryntime in dotnet/runtime#72724 so if/when a net8 build is created the new methods will be used and the workarounds will be ifdeffed out entirely.

Testing on net was done manually with a small repro app that used reflection to force SqlGuidCaster to be compiled. Before these change the reported TypeLoadException was encountered, after them it is not.

/cc @Alerinos @MichalPetryka

[JRahnama]

I will do some changes to this PR, such as the csproj file to include SqlTypeWorkarounds to be included if it is net6 only and changing the Net 8 to net 7 for now.

[Wraith2]

You can't change the net8 to 7 because this is adding support for new apis that aren't in 7. For the rest, go ahead.

[codecov]

Codecov Report

Patch coverage: 45.45% and project coverage change: -0.16 ⚠️

Comparison is base (a4f18ca) 70.82% compared to head (37fb9a0) 70.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1934      +/-   ##
==========================================
- Coverage   70.82%   70.67%   -0.16%     
==========================================
  Files         292      305      +13     
  Lines       61777    61794      +17     
==========================================
- Hits        43752    43670      -82     
- Misses      18025    18124      +99     

Flag	Coverage Δ
addons	92.88% <ø> (+0.49%)	⬆️
netcore	73.43% <45.45%> (-1.01%)	⬇️
netfx	69.27% <ø> (+0.07%)	⬆️

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

Impacted Files	Coverage Δ
...rosoft/Data/SqlTypes/SqlTypeWorkarounds.netcore.cs	94.73% <ø> (+12.91%)	⬆️
...c/Microsoft/Data/SqlClient/Server/ValueUtilsSmi.cs	64.16% <ø> (ø)
...qlClient/src/Microsoft/Data/SqlClient/SqlBuffer.cs	80.45% <ø> (ø)
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	68.58% <45.45%> (-4.81%)	⬇️

... and 93 files with indirect coverage changes

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[David-Engel]

You can't change the net8 to 7 because this is adding support for new apis that aren't in 7. For the rest, go ahead.

The new APIs made it into .net7 last year. I think we are good to go on this PR.
https://github.com/dotnet/runtime/commits/v7.0.0/src/libraries/System.Data.Common/src/System/Data/SQLTypes