Enable a loader, enables a loader for plugins.
The C plugin loader is always enabled. The other plugin loaders are: "gjs", "lua5.1", and "python".
Note that the "python" loader is Python 3 only.
For instance, the following code will enable Python 3 plugins to be loaded:
```c peas_engine_enable_loader (engine, "python"); ```
Note: plugin loaders used to be shared across `PeasEngine`s so enabling a loader on one Engine would enable it on all Engines. This behavior has been kept to avoid breaking applications, however a warning has been added to help applications transition.
| this |
A Engine. |
| loader_name |
The name of the loader to enable. |