RFR: 8303884: jlink --add-options plugin does not allow GNU style options to be provided

[Henry Jen]

Improving plugin option value handling to support passing argument value starts with "--".

Before the fix, in following example, --add-modules will be considered as another option for JLink instead of argument value for --add-options.
--add-options --add-modules=jdk.incubator.concurrent
--add-options=--add-modules=jdk.incubator.concurrent

will cause JLink to report
Error: no value given for --add-options
as --add-modules is considered another option for JLink.

After the fix, by using = will ensure the value is properly handled as argument value. Also using "" with multiple values will be recognized properly. So following form should work
--add-options "--add-modules jdk.incubator.concurrent"
--add-options=--add-modules=jdk.incubator.concurrent

-------------

Commit messages:
 - add test
 - 8303884: jlink --add-options plugin does not allow GNU style options to be provided

Changes: https://git.openjdk.org/jdk/pull/22526/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22526&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303884
  Stats: 157 lines in 2 files changed: 152 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/22526.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22526/head:pull/22526

PR: https://git.openjdk.org/jdk/pull/22526