JDK12 add new method java.lang.String.transform()

[JasonFengJ9]

JDK12 add new method java.lang.String.transform()

Adding java.lang.String.transform() for JDK12.

Manually verified it matches RI results in a simple testcase as following:

    String strOne = "StringOne";
    System.out.println((Object)strOne.transform(string -> string.length()));

Expecting the test coverage is provided by JTReg tests
https://github.com/ibmruntimes/openj9-openjdk-jdk12/blob/e969f57ff8031485b00ccf2ed10f87a627c7bd68/test/jdk/java/lang/String/Transform.java#L24-L28

Related to: #3850

Reviewer: @pshipton
FYI: @DanHeidinga

Signed-off-by: Jason Feng [email protected]

[pshipton]

Please add your test to the test suite.

[pshipton]

Given the implementation is so simple and there is coverage elsewhere, I'll merge without a test.