RFR: 8258411: Move module set configuration from Modules.gmk to conf dir [v2]

[Mandy Chung]

On Tue, 15 Dec 2020 22:58:47 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> `JRE_TOOL_MODULES` started with more than one modules in JDK 9:
>> 
>> JRE_TOOL_MODULES += \
>>     jdk.jdwp.agent \
>>     jdk.pack \
>>     jdk.scripting.nashorn.shell \
>>     #
>> 
>> Since only `jdk.jdwp.agent` one module is left for `JRE_TOOL_MODULES`, as you are refactoring this file, I suggest to get rid of `JRE_TOOL_MODULES` and explicitly name `jdk.jdwp.agent` in `JRE_MODULES`.
>
> Do you see a way to get rid of `DOCS_MODULES` but determine this set at build time?  IIRC it was added for expediency for [JDK-8172312](https://bugs.openjdk.java.net/browse/JDK-8172312).   This is the set of Java SE + JDK modules that excludes `jdk.internal.*` modules and `jdk.unsupported` and also platform-specific modules.   (History: the docs bundle generated prior to JDK 9 only included platform-neutral APIs.)
> 
> As for the conf file for module to class loader mapping, I actually like one single file `jdk-modules.conf` to enumerate all JDK modules.   Currently it only defines the list of modules defined to boot and platform class loader but excludes any modules defined to application class loaders.  I consider to enumerate all modules in this file and the build can verify if any module is missing.
> 
> `module-sets-build.conf` is a bit awkward and I will give more thought on naming ideas.

Can any of `INTERIM_IMAGE_MODULES` , `HOTSPOT_MODULES` and `LANGTOOLS_MODULES` be inlined in the appropriate .gmk file?

`INTERIM_IMAGE_MODULES` is for building interim image.  If it has to be defined in a conf file, I like its name be explicit and match the target or makefile, for example, `interim-images.conf` or `InterimImages.conf`.    This way I can tell what this conf file intends for.  What do you think?

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