Cleanup | Remove unused UDT serialization code

[edwardneal]

Description

This sits alongside #3423. Where the earlier PR widens test coverage of the UDT serialization logic, this one simplifies conditions which are constant at runtime. The two primary variables here are _isTopLevelUdt and _skipNormalize.

_isTopLevelUdt is a readonly variable, which is set in the sole BinaryOrderedUdtNormalizer constructor to a hardcoded value of true. There are then a set of if conditions which test if the variable is false, and which will thus never be called. This PR removes these. The ripple effects of these result in the _padBuffer and _nullInstance variables never being set (and the IsNullable property never being referenced.) These members are also removed.

_skipNormalize is another variable, this time defined on the Normalizer base class. It is only ever set to false, and thus every condition which tests if it is false will succeed. This PR removes the test and runs the code unconditionally.

This accounts for the bulk of the changes. There is one parameter on the constructor to BinaryOrderedUdtNormalizer which is never used, a comment which is incorrect, a call to GetFormat which discards the result, and several fields on SqlUdtInfo which are written to, but never read.

Review of the wider area will highlight some code paths (such as the Size property) which remain unused. There are also quirks such as the use of a per-thread type cache, the implementation of the non-generic IComparable interface, significant numbers of heap allocations, and likely others. The next set/sets of changes will resolve these, so I've deliberately left these alone to keep this PR focused on the removal of dead code paths.

Issues

None.

Testing

All tests pass. I've also tested against the new tests in #3423, and these also pass.

[cheenamalhotra]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 45 lines in your changes missing coverage. Please review.

Project coverage is 60.16%. Comparing base (dc75c40) to head (528ca00).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/Microsoft/Data/SqlClient/Server/SqlNormalizer.cs	0.00%	41 Missing ⚠️
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	1 Missing ⚠️
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	1 Missing ⚠️
...ient/src/Microsoft/Data/SqlClient/Server/SqlSer.cs	0.00%	1 Missing ⚠️
...Client/src/Microsoft/Data/SqlClient/SqlBulkCopy.cs	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (dc75c40) and HEAD (528ca00). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (dc75c40)	HEAD (528ca00)
addons	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3462      +/-   ##
==========================================
- Coverage   65.44%   60.16%   -5.28%     
==========================================
  Files         280      274       -6     
  Lines       62386    62007     -379     
==========================================
- Hits        40828    37308    -3520     
- Misses      21558    24699    +3141     

Flag	Coverage Δ
addons	?
netcore	63.34% <0.00%> (-3.68%)	⬇️
netfx	62.34% <0.00%> (-6.86%)	⬇️

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