Release Note: Shenandoah Changes -Xms to Mean "minimum heap size"

Before the changes in this release, `-Xms` was treated as setting the "initial heap size." This enabled the Shenandoah heap sizing policy to uncommit unused heap that was below that setting. With this release, `-Xms` is treated as providing the "minimum heap size." This change prevents Shenandoah from uncommitting unused heap that is below the `-Xms` setting. `-Xms` can now be used to fine-tune footprint vs. allocation overhead tradeoffs.