Summary
-------

Extend the 'jlink' tool with options to customize the `java.vendor`, `java.vm.vendor` and `java.vendor.url` system properties in the resulting image.

Problem
-------

Downstream distributions of JDK would like to customize system properties related to the vendor information.

Currently the build system supports using `branding.conf` to customize those properties.  However, the `java.vm.vendor` value is hardcoded to "Oracle Corporation" unless the build is configured with the `--with-vendor-name` option.   Also `java.vm.vendor` should have the same default value ("N/A") as the `java.vendor` system property. 

The `jlink` tool can be used to create a custom run-time image with altered values for several "java.vendor.*" system properties, but is missing the capability to update `java.vendor`, `java.vm.vendor` and `java.vendor.url` system properties.

Solution
--------

Define new `jlink` plugins to implement the desired options. The default value for `java.vm.vendor` is "N/A", the same default value as `java.vendor`.

Specification
-------------

The new jlink plugins will implement the following options:

  - `--vendor=<vendor>` override the vendor string baked into the build, if any. The value of the system property "java.vendor" will be `<vendor>`.

  - `--vendor-url=<vendor-url>` override the vendor URL baked into the build.  The value of the system property "java.vendor.url" will be `<vendor-url>`.

  - `--vendor-vm <vendor>` override the vendor string baked into the build, if any. The value of the system property "java.vm.vendor" will be `<vendor>`.

Example usage:

```
$ jlink --add-modules java.base --output /tmp/jre --vendor 'Example Corp.' --vendor-url https://example.com --vendor-vm 'Example VM'
$ /tmp/jre/bin/java -XshowSettings:properties --version 2>&1 | grep -i example
    java.vendor = Example Corp.
    java.vendor.url = https://example.com
    java.vm.vendor = Example VM
$
```

In addition, the value of `java.vm.vendor` system property is "N/A" by default unless the build is configured with `--with-vendor-name` option to specify the vendor which will be set in `java.vendor` and `java.vm.vendor`.