RFR: 8258411: Move module set configuration from Modules.gmk to conf dir [v4]

[Magnus Ihse Bursie]

> 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:

  Rename configuration files

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1781/files
  - new: https://git.openjdk.java.net/jdk/pull/1781/files/ef9d53cb..199832a1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1781&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1781&range=02-03

  Stats: 3 lines in 4 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1781.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1781/head:pull/1781

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