docs: add XML documentation for CMS CompressedData (Batch 15d)

[KonradSop]

Description

Adds XML documentation to CmsCompressedData — the read-side entry point for CMS CompressedData messages:

• Class summary — parse and decompress via GetContent() or GetContentStream().
• Constructors — byte array, stream, and ContentInfo overloads; ArgumentNullException on the
  core constructor.
• Properties and accessors — content types, decompressed content (with optional size limit),
  underlying structures, and DER encoding.

Legacy /** block comments converted to XML.

Key Accomplishments

• Compressed-data discoverability: IDE tooltips now cover the full public read-side surface.
• Accurate exception contracts: CmsException documented on decompress paths; size-limit overload
  notes a possible StreamOverflowException inner exception.
• Focused scope: single file; no behavioural or signature changes.
• Documentation quality: all new or modified XML documentation lines are at most 120 characters.

Verification

• Build Status: dotnet build crypto/src/BouncyCastle.Crypto.csproj -c Release — 0 errors, no new warnings.
• Scope: Documentation-only; no behavioural or signature changes.

Checklist before requesting a review

• I have performed a self-review of my code
• I have kept the patch limited to only change the parts related to the patch
• This change requires a documentation update

See also Contributing Guidelines.