Document the new VcpkgInstalledDirRoot property

[stinos]

See microsoft/vcpkg#49738.

[learn-build-service-prod]

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[learn-build-service-prod]

Learn Build status updates of commit 2462269:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/users/buildsystems/msbuild-integration.md	✅Succeeded	View

For more details, please refer to the build report.

[vicroms]

Made some style changes.

[learn-build-service-prod]

Learn Build status updates of commit 0644eec:

✅ Validation status: passed

File	Status	Preview URL	Details
vcpkg/users/buildsystems/msbuild-integration.md	✅Succeeded	View

For more details, please refer to the build report.

[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[stinos]

Proposed changes make sense so updated and rebased. Except for the proposed change to line 243 because it's not strictly related to this PR and seems more fit for a broader 'improve style/readability' (e.g. perhaps the change was proposed to make the sentence start with a capital but there's at least 1 other sentence which also start with vcpkg).