RFR JDK-8236688 Clarify String::indent javadoc (CSR)

[Jim Laskey]

Please review this CSR to clarify the javadoc details of String::indent (proposed by Andrew Leonard).

webrev: http://cr.openjdk.java.net/~jlaskey/8230800/webrev.00/index.html <http://cr.openjdk.java.net/~jlaskey/8230800/webrev.00/index.html>
csr: https://bugs.openjdk.java.net/browse/JDK-8236688
jbs: https://bugs.openjdk.java.net/browse/JDK-8230800