Reuse properties in VersionPrefix (#5443)

Author: eerhardt

eng/Versions.props

@@ -4,7 +4,7 @@
     <MajorVersion>9</MajorVersion>
     <MinorVersion>0</MinorVersion>
     <PatchVersion>0</PatchVersion>
-    <VersionPrefix>9.0.0</VersionPrefix>
+    <VersionPrefix>$(MajorVersion).$(MinorVersion).$(PatchVersion)</VersionPrefix>
     <PreReleaseVersionLabel>preview.1</PreReleaseVersionLabel>
     <!--
       When running package validation as part of the build, we want to ensure we didn't break the API against the previous