Remove workarounds and cleanup source to meet dotnet/runtime analyzer requirements.

[maryamariyan]

Keeping track of miscellaneous cleanup tasks leftover from Extensions consolidation:

Code Cleanups:

• Move shared files between Configuration projects to Common folder (Microsoft.Extensions.Configuration: enabling FileExtensions/Ini #33844 (comment)) -> (addressed by Minor cleanup on Extensions in Configuration #42788)
• Delete duplicate files or those not used (Enable Microsoft.Extensions.DependencyInjection #33816 (comment)) (addressed by Remove AspNetCore Testing Infra that isn't used #40091)
• Removing styling and whitespace nit errors skipped using NoWarns (refer to Directory.Build.props)

Leftover PR feedback:

• Remove files: Bring commit history for more files from Extensions repo #33494 (comment) (addressed by Remove AspNetCore Testing Infra that isn't used #40091)

Tests:

• Enable Performance tests into dotnet/performance repo:
  Primitives: Adds Microsoft.Extensions.Primitives benchmarks to perf repo performance#1288
  Later: DI, Logging and Hosting
• Enable DI perf tests requiring InternalsVisibleTo - covered by Remove INTERNAL_DI from DI tests performance#1583
• Enable FunctionalTests/TestApp on Hosting: Enable FunctionalTests/TestApp on Extensions Hosting #34090

Docs:

Migrate docs from source -> docs repo

It looks like extensions is still using in-source triple-slash docs. We should work with @carlossanlop to do a one time insertion of these to the docs-repo then set up the packages to consume the docs from docs repo.

• Microsoft Extensions Logging docs dotnet-api-docs#4104
• Adds docs for Microsoft.Extensions.Primitives dotnet-api-docs#4105
• Extensions: DI, Configuration, Caching.Memory docs dotnet-api-docs#4107
• Docs for Extensions: FileProviders and Hosting dotnet-api-docs#4106

[maryamariyan]

closing as remaining work is covered by other issues now.