feat: Microsoft.DocAsCode.* -> Docfx.*

[yufeih]

• Changes package name from Microsoft.DocAsCode.* to Docfx.*
• Changes namespaces from Microsoft.DocAsCode.* to Docfx.*
• Disables package validation until we publish a Docfx.App package.

#8930

[codecov]

Codecov Report

Patch coverage: 91.04% and project coverage change: -0.01 ⚠️

Comparison is base (bdd5161) 76.89% compared to head (198100a) 76.89%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8943      +/-   ##
==========================================
- Coverage   76.89%   76.89%   -0.01%     
==========================================
  Files         605      605              
  Lines       25074    25074              
==========================================
- Hits        19281    19280       -1     
- Misses       5793     5794       +1     

Impacted Files	Coverage Δ
...rationLevelRestApi/SplitRestApiToOperationLevel.cs	98.07% <ø> (ø)
...fx.Build.TagLevelRestApi/SplitRestApiToTagLevel.cs	96.00% <ø> (ø)
src/Docfx.App/BuildOptions.cs	100.00% <ø> (ø)
src/Docfx.App/Config/BuildJsonConfig.cs	86.11% <ø> (ø)
src/Docfx.App/Config/ContentPairingInfo.cs	0.00% <ø> (ø)
src/Docfx.App/Config/FileMetadataPairs.cs	66.66% <ø> (ø)
src/Docfx.App/Config/FileMetadataPairsConverter.cs	83.33% <ø> (ø)
src/Docfx.App/Config/FileMetadataPairsItem.cs	100.00% <ø> (ø)
src/Docfx.App/Config/GroupConfig.cs	0.00% <ø> (ø)
src/Docfx.App/Config/ListWithStringFallback.cs	100.00% <ø> (ø)
... and 223 more

... and 704 files with indirect coverage changes

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