build: Add Meson glue to let building TinySPARQL as a subproject
This meson.override_dependency() allows other projects using the Meson build system to compile TinySPARQL as a subproject through a Meson wrap file, e.g.:
[wrap-git]
directory = tinysparql
url = https://gitlab.gnome.org/GNOME/tinysparql.git
revision = main
depth = 1
On a subprojects/tinysparql-3.0.wrap file, and dependency() will automatically handle falling back to using the subproject if the system does not meet the dependency and required version.
Edited by Carlos Garnacho