merge wrappers into contained placeholder

[jenseng]

Spawned from #3

If all that a wrapper contains is a placeholder (no text content), we should not create a wrapper and should instead merge its component(s) into the placeholder value, e.g. consider:

<p translate="yes">Hello <b>{user}</b></p>

Ideally that should yield the following (note the lack of wrapper):

"Hello %{user}"

The value for %{user} would be <b>{user}</b>

[jenseng]

upon adding a failing test i realized it actually does this already, except that, the placeholder is poorly named (e.g. <b>{user}</b> => %{b_user}) ... so maybe we just need better inferred placeholders