libcamera/base: Introduce new base library

The libcamera-base.so will feature internal support functionality
that is utilised by libcamera, and can be shared in other places.

This new library provides a layer beneath libcamera which provides
common abstractions to internal objects.

A pkg-config file is generated and named libcamera-base.pc which allows
components such as external IPA modules to link directly to this library
if they need. Normal applications will reference this library through
the Requires: statement provided by the libcamera.pc package
configuration, and linkage will be handled automatically through the
pkg-config mechanisms.

No code is moved to this library yet, this patch only introduces the
framework, construction and linkage.

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

Documentation/meson.build

@@ -22,6 +22,8 @@ if doxygen.found() and dot.found()
     custom_target('doxygen',
                   input : [
                       doxyfile,
+                      libcamera_base_headers,
+                      libcamera_base_sources,
                       libcamera_internal_headers,
                       libcamera_ipa_headers,
                       libcamera_ipa_interfaces,