doc: align module capitalization

[Flameopathic]

changes:

• adds required meta.name attribute
• implements check for module documentation title matching module name
• implements specific error for module metadata missing required attributes
• adds meta.name attribute to all applicable meta files
• NVF -> nvf and Nixvim -> NixVim
• documents meta.name attribute

related: #1084

Things done

• Tested locally
• Tested in testbed
• Commit message follows commit convention
• Fits style guide
• Respects license of any existing code used

Notify maintainers

[Flameopathic]

as an aside, we should consider breaking docs/default.nix into multiple files. as it stands, it is unwieldy and difficult to read.

[trueNAHO]

Overall approach LGTM.

[danth]

The way the index works means the links in the sidebar are sorted into alphabetical order based on the module slug: it would be nice to change that to use the human readable name at some point. Not necessary in this PR though.

[awwpotato]

lgtm