RFR: 8257726: Make -XX:+StressLdcRewrite option a diagnostic option

[Coleen Phillimore]

See bug for details.  Tested:

$ java -XX:+StressLdcRewrite -version
Error: VM option 'StressLdcRewrite' is diagnostic and must be enabled via -XX:+UnlockDiagnosticVMOptions.
Error: The unlock option must precede 'StressLdcRewrite'.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
$ java -XX:+UnlockDiagnosticVMOptions -XX:+StressLdcRewrite -version
openjdk version "16-internal" 2021-03-16
OpenJDK Runtime Environment (build 16-internal+0-2020-12-15-1356558.coleen...)
OpenJDK 64-Bit Server VM (build 16-internal+0-2020-12-15-1356558.coleen..., mixed mode, sharing)

Also, java/lang/instrument which has a test using StressLdcRewrite and tier1.

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Commit messages:
 - 8257726: Make -XX:+StressLdcRewrite option a diagnostic option
 - 8257726: Make -XX:+StressLdcRewrite option a diagnostic option

Changes: https://git.openjdk.java.net/jdk/pull/1783/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1783&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257726
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1783.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1783/head:pull/1783

PR: https://git.openjdk.java.net/jdk/pull/1783