Consistent dynamic param usage in components with bindings

[maximepvrt]

Some component params are passed via the block (::alert{:type="type"}), while others require {{$doc.meta.param}} in bindings.

Example:

---
type: "warning"
---

::alert{:type="type"}
Your warning
::

{{type}}:{{$doc.meta.type}}

<alert type="warning">
Your warning
</alert>

:warning

Proposal: harmonize so that dynamic params work consistently both in component blocks and in bindings.