RFR: 8258411: Move module set configuration from Modules.gmk to conf dir [v5]

[Mandy Chung]

On Wed, 16 Dec 2020 18:36:25 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> The hard-coded list of modules in `make/common/Modules.gmk` has always been a wart in the build system. We pride ourself on using discovery instead of hard-coded list. In this case, it is not possible to do do auto-discovery, since the different module sets are configured, not determined.
>> 
>> Thus the actual lists of module sets should move to the `make/conf` directory.
>> 
>> This is the first patch in a series where I will move configuration values spread over the build system into the designated `make/conf` directory.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Changes as requested by reviewers

Marked as reviewed by mchung (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1781