Trim XML documentation for reference project + fix Note tags

[cheenamalhotra]

Fixes #3228

Modified:

• <note> tags are not recognized by mdoc that generates .NET API Reference documentation, hence reverted them back to Markdown formatted notes.
• Remarks and Examples make VS Intellisense too long, for even System.Runtime APIs don't contain them. This PR trims them down from XML docs file included in the 'ref' directory that's used by VS Intellisense. The root 'lib' directory's XML files contains full docs that are picked up to be published at .NET API Reference.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.70%. Comparing base (f3ae72a) to head (a2ba4f0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3233      +/-   ##
==========================================
- Coverage   72.73%   72.70%   -0.04%     
==========================================
  Files         288      303      +15     
  Lines       59527    59527              
==========================================
- Hits        43298    43280      -18     
- Misses      16229    16247      +18     

Flag	Coverage Δ
addons	92.58% <ø> (ø)
netcore	75.14% <ø> (-0.05%)	⬇️
netfx	71.36% <ø> (-0.02%)	⬇️

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