Dplug v14 propositions

[p0nce]

• dplug:host must be nothrow @nogc like other parts of Dplug #787 nothrow @nogc dplug:host sub-package, fortunately probably no users of it other than Dplug tools
• Wren RGBA needed functions #785 RGBA utilities => is an addition, post-poned
• Deprecate much more stuff in dplug.graphics.draw, host the strangest functions in their point of use (such as UIKnob)
• remove all deprecated stuff.
• legacyMouseCursor should be replaced by a permanent Dplug_NoMouseCursor if like me you do not want to deal with mouse cursors for now
• Progress towards less phobos and exceptions
• deprecate/remove the dplug:core "runtime section"
• deprecate/remove the dplug:core stackallocator.d
• implement Vec more like std::vector in MSVC, with two pointers and similar growth policy maybe (or the one in druntime which is clever) => well no breakage needed, post-poned