Update all documentation version references to match current 2.2.0 release

[Copilot]

This PR updates all documentation files to ensure they accurately reflect the current version 2.2.0 of the Firely CQL SDK and correct dependency versions.

Issues Fixed

The documentation contained several outdated version references that were inconsistent with the actual project configuration:

1. Main README version mismatch: The README stated "This is release version 2.1 of the engine" while the actual version in cql-sdk.props is 2.2.0
2. Example project version references: Both CqlSdkExamples and CqlSdkExamplesPreview projects had commented package references pointing to outdated 2.1.0 versions
3. FHIR dependency version discrepancy: The README listed Hl7.Fhir.Base as version 5.12.0, but the actual version configured in cql-base.props is 6.0.0

Changes Made

Version Updates

• Updated main README.md to correctly state "This is release version 2.2 of the engine"
• Updated all commented Hl7.Cql.Invocation package references in example projects from 2.1.0 to 2.2.0

Dependency Documentation Updates

• Corrected Hl7.Fhir.Base version from 5.12.0 to 6.0.0 to match the FirelySdkVersion property
• Updated all Hl7.Fhir.R4 references from generic "Firely SDK version" to explicit "Version 6.0.0"

Verification

• All version references now accurately reflect the current project configuration
• Build verification confirms the project continues to compile successfully
• No outdated version references remain in documentation files

This ensures that users and developers have accurate, up-to-date information about the SDK version and its dependencies when referencing the documentation.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update all documentation</issue_title>
<issue_description>Ensure all documentation files are up to date with changes that have been made since the last time they were updated.

Example, updating the version to 2.2.0 where it mentions an outdated one. </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #1049

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.