Better placement of meta files for configuration metadata (for translation)

1. meta location and names

Here are the current locations, and names, of the meta files that the patch adds from #1648930-247: Introduce configuration schema and use for translation. Just documenting it. Not lobbying for it.

Generated this list with: $ grep yml config_metadata-1648930-247.patch | grep +++ | cut -f2 -d" " | sed 'sxb/xx'

core/modules/contact/meta/contact.category.%.yml
core/modules/image/meta/image.effect.image_crop.yml
core/modules/image/meta/image.effect.image_resize.yml
core/modules/image/meta/image.effect.image_rotate.yml
core/modules/image/meta/image.effect.image_scale.yml
core/modules/image/meta/image.effect.image_scale_and_crop.yml
core/modules/image/meta/image.style.%.yml
core/modules/system/meta/system.maintenance.yml
core/modules/system/meta/system.site.yml
core/modules/user/meta/user.mail.yml

2. an (*the*) include in a meta

We have one (or so grep says) example with an include:

$ grep -R include core/modules/*/meta/*.yml 
core/modules/image/meta/image.style.%.yml:      .include: 'image.effect.[%parent.name]'

3. config names and locations

Here are the config names and locations (at least at the time of this posting)

core/modules/contact/config/contact.category.feedback.yml
core/modules/contact/config/contact.settings.yml
core/modules/image/config/image.settings.yml
core/modules/image/config/image.style.large.yml
core/modules/image/config/image.style.medium.yml
core/modules/image/config/image.style.thumbnail.yml
core/modules/system/config/system.authorize.yml
core/modules/system/config/system.cron.yml
core/modules/system/config/system.filter.yml
core/modules/system/config/system.logging.yml
core/modules/system/config/system.maintenance.yml
core/modules/system/config/system.menu.yml
core/modules/system/config/system.module.yml
core/modules/system/config/system.performance.yml
core/modules/system/config/system.rss.yml
core/modules/system/config/system.site.yml
core/modules/system/config/system.theme.yml
core/modules/user/config/user.block.yml
core/modules/user/config/user.flood.yml
core/modules/user/config/user.mail.yml
core/modules/user/config/user.settings.yml

I'm a little less clear on location, so I didn't add much history. Please feel free to add any history you think is relevant, or just add new ideas.
The new include format I think helped reduce some concerns about implying merging based on location.

222.

names and % patterns
#1648930-222: Introduce configuration schema and use for translation by @Jose Reyero

Example: image.effect.image_scale.yml
• Note this adds an explicit 'include' for the common image.effect properties (% is not replaced anymore)
• We are doing nested includes here: 'image.style.%' includes 'image.effect.[name]' which includes 'image.effect.%'

237.

#1648930-237: Introduce configuration schema and use for translation
@effulgentsia

, it now seems odd to me that we have .definition inside the yaml files, but the folder name is meta. Can we rename to definition? I also find it odd for this folder to be outside of the config directory. If it's possible to move into the config directory without messing up existing CMI code, let's do that. Otherwise, how about renaming it to config_definition until such time as we're able to move it inside?

238.

#1648930-238: Introduce configuration schema and use for translation
@sun

Neither ./meta nor ./definition directories really make sense to me. I'd actually prefer to go back to to '.meta' keys in the metadata files, just because it's shorter and equally gets the point across. And in light of that and earlier comments, a ./meta directory within an extension doesn't really make sense, because there is no relationship to config there. I'd see two possible resolutions: 1) Either change ./meta into ./meta/config on the grounds/idea that we might have further stuff that could use metadata like this, 2) Move ./meta into ./config/meta (inherently accepting the fact that this would prevent a "meta" context to exist for configuration, since all subdirectories should be considered as context override sources).