use a vendored recastnavigation
there is a consensus on the fact that recastnavigation should be bundled with each project that use it, and should not be provided as a shared library package (as this is upstream's recommendation & they make no promises about ABI stability)
to quote smcv: that's a vendorable "copylib" like libglnx or libegg, not something that Policy demands we de-vendor like a bundled zlib
so here is my proposal for OpenMW:
- stop depending on
librecast-dev
- add a new component/upstream-tarballs (uscan will generate it for us)
- patch the build system to use this code and don't download any copy from the network