Remove obsolete warning suppression. and fix deprecated APIs

[filzrev]

This PR contains following changes.

• Remove CS0612/CS0618 (Type or member is obsolete) solution-wide warning suppression.
• Replace deprecated APIs (Newtonsoft.Json and YamlDotNet) to supported API that is suggested by intellisense.
• Set file-level warning suppression that need to use obsolete property for compatibility purpose.
• Set [Obsolete] attribute to test code that tests obsolete code.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (43bda19) 76.90% compared to head (2c1fa83) 76.90%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8937   +/-   ##
=======================================
  Coverage   76.90%   76.90%           
=======================================
  Files         605      605           
  Lines       25091    25088    -3     
=======================================
- Hits        19296    19294    -2     
+ Misses       5795     5794    -1     

Impacted Files	Coverage Δ
...icrosoft.DocAsCode.Build.Engine/ManifestUtility.cs	76.74% <ø> (ø)
...ft.DocAsCode.Build.Engine/SingleDocumentBuilder.cs	82.87% <ø> (ø)
src/Microsoft.DocAsCode.Common/JsonUtility.cs	100.00% <100.00%> (ø)
...rializers/EmitGenericCollectionNodeDeserializer.cs	90.56% <100.00%> (ø)
...rializers/EmitGenericDictionaryNodeDeserializer.cs	64.00% <100.00%> (ø)
...eDeserializers/ExtensibleObjectNodeDeserializer.cs	77.77% <100.00%> (-0.80%)	⬇️
...rsalStrategies/FullObjectGraphTraversalStrategy.cs	93.10% <100.00%> (ø)
...ft.DocAsCode.YamlSerialization/YamlDeserializer.cs	86.92% <100.00%> (-0.20%)	⬇️
...soft.DocAsCode.YamlSerialization/YamlSerializer.cs	68.85% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[yufeih]

Looks great! Thank you @filzrev !