docs: add XML documentation for CMS attribute and originator generators (Batch 16d)

[KonradSop]

Description

Adds XML documentation to CMS write-side attribute generators and related helpers:

• OriginatorInfoGenerator - builds OriginatorInfo from certificate/CRL stores; links to
  OriginatorInformation.
• SimpleAttributeTableGenerator - fixed attribute table for unsigned/preconfigured attributes.
• DefaultSignedAttributeTableGenerator - expanded class summary; fixed broken <see cref> typo;
  <param>/<returns> on GetAttributes.
• DefaultAuthenticatedAttributeTableGenerator - expanded class summary; <param>/<returns> on
  GetAttributes.
• CmsCompressedDataGenerator - completed public surface; <exception> on Generate.

Legacy /** block comments converted to XML where present.

Key Accomplishments

• CMS attribute discoverability: IDE tooltips cover default signed/authenticated attribute
  generation and originator info construction.
• Accurate exception contracts: documented only on CmsCompressedDataGenerator.Generate.
• Focused bundle: five related CMS generator files; no behavioural or signature changes.
• Documentation quality: all new or modified /// 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.