RFR 8214971 : Replace use of string.equals("") with isEmpty()

[Roger Riggs]

Please review changing string.equals("") to string.isEmpty().
isEmpty is preferred, performs better and is easier to optimize.

The change is a literal substitution in all files and only in these modules:

    java.base
    java.logging
    java.management
    java.management.rmi
    java.naming
    java.net.http
    java.prefs
    java.rmi
    java.scripting
    java.sql
    java.sql.rowset
    java.xml
    jdk.jartool
    jdk.javadoc
    jdk.jcmd
    jdk.jconsole
    jdk.management.agent
    jdk.naming.dns
    jdk.rmic


Webrev:
http://cr.openjdk.java.net/~rriggs/webrev-string-isempty-8214971-1/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8214971

Thanks, Roger