Now meson offers a pkgconfig module to automate the generation of *.pc
files. These mechanism also automatically generates *-uninstalled.pc,
which are useful for uninstalled setups (common in CI and development
environments).
This patch updates the generation of *.pc files using the meson module
rather than manual generation.
In order to use libva in a subproject[1] or in an "uninstalled"
environment, libva needs to fix its public headers layout in its
source directory. A previous fix was proposed[2] which moved
those headers as expected, but it was closed because it was too
invasive.
This new approach is less invasive and oriented to meson subprojects
or uninstalled setups, which has a wider audience.
The fix is two-fold:
1. Bump the required version of meson in order to support this new
feature. And update deprecated syntax.
2. Copy each public header file into subproject's build directory.
