NativeAOT | Remove DataSet.ReadXml, correct type name

[edwardneal]

Description

This PR's diff is much smaller than it looks! There's an embedded XML resource, and adjusting this meant that the indentation levels changed. When that's accounted for, the PR becomes much smaller - around 300 lines, rather than 7800.

This PR relates to #1942 and #1261. At present, there are two identical copies of the Microsoft.Data.SqlClient.SqlMetaData.xml embedded resource in the netfx and the netcore projects. This PR merges these with a single file. More importantly though, this embedded resource is used only within DbMetaDataFactory; it's deserialized using DataSet.ReadXml, where it is eventually used in SqlConnection.GetSchema.

DataSet.ReadXml isn't trim-safe - it uses XML serialization in the background. I've replaced this with a simple parsing routine which runs against the embedded resource and adds the rows manually.

The net result is smaller, faster and more efficient. Sizoscope confirms that this PR cuts the file size of a simple application by 3.8MB, from 20.4MB to 16.6MB. Benchmark results for this in isolation are:

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
Before	1,819.7 μs	25.07 μs	23.45 μs	1.00	0.02	187.5000	39.0625	829.81 KB	1.00
After	738.9 μs	3.25 μs	2.71 μs	0.41	0.01	62.5000	19.5313	307.74 KB	0.37

Separately, I noticed that my earlier PR #3309 generated two warnings when publishing because it wasn't using a fully-qualified type name. I've adjusted this.

Issues

Relates to #1942.
Relates to #1261.
Follows up #3309.

Testing

All tests continue to pass.

There's a lot of validation of the structure of the XML in the embedded resource, and this is done with debug assertions. I've treated this as hardcoded at the point of build, so haven't used exceptions for this. I can change this if needed.

[mdaigle]

A few questions to help with my understanding

[paulmedynski]

Asking for some clarification on why we're reading this XML at runtime.

[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.22%. Comparing base (832e8da) to head (21cad07).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3369      +/-   ##
==========================================
- Coverage   65.12%   62.22%   -2.90%     
==========================================
  Files         300      294       -6     
  Lines       65379    65183     -196     
==========================================
- Hits        42578    40563    -2015     
- Misses      22801    24620    +1819     

Flag	Coverage Δ
addons	?
netcore	66.64% <100.00%> (-1.70%)	⬇️
netfx	60.84% <100.00%> (-5.54%)	⬇️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.