CDS module graph support for --module and --modulepath

CDS full module graph should be improved to support the following scenarios (where FMG is currently disabled):

1. At runtime, --module is specified.

This limits the number of modules visible in the boot layer. We should load the FMG from CDS, and then trim out the unwanted modules.

2. At dump time, --module is specified

This limits the number of modules visible in the boot layer. At runtime, we require that the same --module must be specified in order to load the FMG.

3. At runtime, --module-path is specified.

We should load the FMG from CDS, and then add the extra modules.

4. At dump time, --module-path is specified

We should dump the FMG with the extra modules. At run time, we require that --module-path is the same as (or a superset of) the dump time --module-path in order to load the FMG.

This RFE can be implemented in several steps (to be tracked as subtasks).