runtime(yaml): fix wrong order of undo_ftplugin suboptions

runtime(yaml): fix wrong order of undo_ftplugin suboptions

This commit fixes the following error message:
```
Compiler not supported: make inc< sw< sts<
```

1. orginal value: `setl com< cms< et< fo<| compiler make inc< sw< sts<`
2. correct value: `setl com< cms< et< fo< inc< sw< sts< | compiler make`

While at it, let's also document the g:yaml_recommended_style variable.

closes: #17179

Co-authored-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Vincent Law <vlaw@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>