Revert "Perf | avoid boxing of SqlGuid in SqlBuffer (#2306)"

[ErikEJ]

This reverts commit 9602271.

(Which had bugs and very low test coverage)

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (838b931) 72.50% compared to head (a270a02) 72.48%.

Files	Patch %	Lines
...osoft/Data/SqlClient/Server/ValueUtilsSmi.netfx.cs	0.00%	2 Missing ⚠️
...qlClient/src/Microsoft/Data/SqlClient/SqlBuffer.cs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2311      +/-   ##
==========================================
- Coverage   72.50%   72.48%   -0.02%     
==========================================
  Files         310      310              
  Lines       61872    61873       +1     
==========================================
- Hits        44858    44847      -11     
- Misses      17014    17026      +12     

Flag	Coverage Δ
addons	92.88% <ø> (ø)
netcore	76.70% <66.66%> (-0.01%)	⬇️
netfx	69.92% <40.00%> (-0.02%)	⬇️

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