Help windows do not inherit `NormalFloat` highlight

[akinsho]

The highlights for the help menu don't match the same highlights used for the agenda/capture (if those are set to floats)

Other than the win_split_mode = 'float' and the border I haven't changed anything window related so I think the highlights just have different values set 🤔

Originally posted by @akinsho in https://github.com/nvim-orgmode/orgmode/issues/509#issuecomment-1445038705

[kristijanhusak]

You are right, in some places we do winhl as Normal:Normal, while in other places we don't. I'm not sure which one of these options would be more preferred, I'm open for suggestions:

• Remove all winhl, use what user is generally using for NormalFloat
• Set Normal:Normal on all popup windows

[akinsho]

@kristijanhusak a pattern I've seen a lot of and is the best solution IMO is to link highlights to some custom highlight of yours that is advertised in the docs and linked as default e.g. Normal:OrgmodeNormal this allows the user to easily override the win highlights

[akinsho]

A smaller simpler solution is just to default to float normal, but the user then has no way to set their preferences