8231556: Wrong font ligatures used when 2 versions of same font used

Backport-of: d86eb1d

src/java.desktop/share/classes/sun/font/PhysicalFont.java

@@ -41,12 +41,19 @@ public abstract class PhysicalFont extends Font2D {
     protected Object nativeNames;
 
     public boolean equals(Object o) {
-        return (o != null && o.getClass() == this.getClass() &&
-                ((Font2D)o).fullName.equals(this.fullName));
+        if (o == null || o.getClass() != this.getClass()) {
+            return false;
+        }
+        PhysicalFont other = (PhysicalFont)o;
+        return
+           (this.fullName.equals(other.fullName)) &&
+            ((this.platName == null && other.platName == null) ||
+             (this.platName != null && this.platName.equals(other.platName)));
     }
 
     public int hashCode() {
-        return fullName.hashCode();
+        return fullName.hashCode() +
+               (platName != null ? platName.hashCode() : 0);
     }
 
     /**