meson: Rename variables storing headers lists

The list of public, IPA and internal header files are stored in three
meson variables, named libcamera_api, libcamera_ipa_api and
libcamera_headers respectively. The lack of uniformity is a bit
confusing. Fix it by renaming those variables to
libcamera_public_headers, libcamera_ipa_headers and
libcamera_internal_headers.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Jacopo Mondi <jacopo@jmondi.org>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/ipa/meson.build

@@ -1,10 +1,10 @@
 # SPDX-License-Identifier: CC0-1.0
 
-libcamera_ipa_api = files([
+libcamera_ipa_headers = files([
     'ipa_controls.h',
     'ipa_interface.h',
     'ipa_module_info.h',
 ])
 
-install_headers(libcamera_ipa_api,
+install_headers(libcamera_ipa_headers,
                 subdir: join_paths(libcamera_include_dir, 'ipa'))