Tidy up advanced connection settings

The advanced tor connection settings, under "Advanced > Settings…" could use a little love:

1. The proxy type selector is empty initially.
2. The proxy type selector is left-aligned, far from its label.
3. Spacing and alignment is a bit awkward.
4. We do not validate the input values, which can either lead to the settings being discarded (e.g. setting the proxy port to be 0) or the settings failing to be parsed by the tor process. See related #43405 (closed).

Maybe a low priority given this is labelled "Advanced".

We could possibly split out the validation into another issue if we want to handle it separately.

/cc @morgan @donuts @felicia