Add docs for requested features with platform expressions

[autoantwort]

For microsoft/vcpkg-tool#813

Original documentation PR microsoft/vcpkg#27917

Drive by fix for: #98

[prmerger-automator]

@autoantwort : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit d9363cc:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/reference/vcpkg-json.md	✅Succeeded	View

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[vicroms]

Some suggestions

[learn-build-service-prod]

Learn Build status updates of commit 0501ac6:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/reference/vcpkg-json.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit e148fbb:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/reference/vcpkg-json.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit b775da6:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/reference/vcpkg-json.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel