docs: implement review comments

- documentation of enums, constants and signals are seperated
- usage of exhale is avoided and the API documentation is generated by
the manual rst files
- Lua API documentation is modified using breathe
- remove exhale usage and exhale dependencies
- remove session bin related rst files and modify the build files
accordingly.
2 jobs for wp-doc-dev-branch in 7 minutes and 39 seconds
latest
Status Job ID Name Coverage
  Container
passed #9594389
container_fedora

00:05:59

 
  Build
passed #9594390
build_on_fedora

00:01:40