modules: add combine-stream module

The module can:

- Make a sink that sends all or some channels to other sinks.
- Make a source that combines multiple sources into one.

The selection of what streams to combine is implemented with rules so
that the selection is very configurable. By default all Audio/Sink or
Audio/Source nodes are selected.

doc/pipewire-modules.dox

@@ -54,6 +54,7 @@ List of known modules:
 - \subpage page_module_avb
 - \subpage page_module_client_device
 - \subpage page_module_client_node
+- \subpage page_module_combine_stream
 - \subpage page_module_echo_cancel
 - \subpage page_module_example_sink
 - \subpage page_module_example_source

src/modules/meson.build

@@ -8,6 +8,7 @@ module_sources = [
   'module-avb.c',
   'module-client-device.c',
   'module-client-node.c',
+  'module-combine-stream.c',
   'module-echo-cancel.c',
   'module-example-sink.c',
   'module-example-source.c',
@@ -135,6 +136,15 @@ pipewire_module_echo_cancel_sources = [
   'module-echo-cancel.c',
 ]
 
+pipewire_module_combine_stream = shared_library('pipewire-module-combine-stream',
+  [ 'module-combine-stream.c' ],
+  include_directories : [configinc],
+  install : false,
+  install_dir : modules_install_dir,
+  install_rpath: modules_install_dir,
+  dependencies : [spa_dep, dl_lib, pipewire_dep],
+)
+
 pipewire_module_echo_cancel = shared_library('pipewire-module-echo-cancel',
   pipewire_module_echo_cancel_sources,
   include_directories : [configinc],