* Write source map without creating temp file
Less I/O, and one less place where we access the global path helpers.
* Drop useless app_path() helper
This was probably taken straight from Laravel. There is no equivalent
concept in Flarum, so this should be safe to remove.
* Deprecate global path helpers
Developers using these helpers can inject the `Paths` class instead.
* Stop storing paths as strings in container
* Avoid using path helpers from Application class
* Deprecate path helpers from Application class
* Avoid using public_path() in prerequisite check
a) The comparison was already outdated, as a different path was passed.
b) We're trying to get rid of these global helpers.
