Building vmtx from features.fea

Currently when including vmtx in features.fea it raises an error that the functionality is unsupported:
```
INFO:ufo2ft:Building OpenType tables
INFO:ufo2ft.outlineCompiler:The copyright was normalized for storage in the CFF table and consequently some characters were dropped: 'Copyright 2022-2023 The Unbounded Sans Project Authors https:github.comNightFurySL2001unbounded-sans
Copyright 2020 The Dela Sans Project Authors https:github.comsyakuzenDelaGothic'
fontmake: Error: In 'UnboundedSans.ufo': Compiling UFO failed: UnboundedSans.ufo\features.fea:28:1: "table vmtx" is not supported
```

Will there be support for [vmtx in features.fea](https://adobe-type-tools.github.io/afdko/OpenTypeFeatureFileSpecification.html#9.h) soon? It will be immensely useful to use the features.fea method since the alternative is to modify all the glifs in UFO to include height and public.verticalOrigin.

Also vhea support might crash with #586 so that might need to be looked into too.