[rhel-9] Adopt JAVA_MAX_MEM_RATIO changes from OPENJDK-1510 for consistency

The fix for OPENJDK-1510 changes the way that JAVA_MAX_MEM_RATIO is managed.
The user-supplied value has any fractional value removed and the result is
presented to the JVM as a float. This was needed for JDK8 (which only accepts
float-format numbers for -XX:MaxRAMPercentage) which is not relevant for the
UBI9 images (where we don't ship JDK8 flavours). However we should port it
over for consistency.