Clean up usages / deprecate path helpers (#2155)

* 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a) The comparison was already outdated, as a different path was passed.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.

src/Foundation/Application.php

@@ -86,8 +86,6 @@ class Application
         $this->registerBaseBindings();
         $this->registerBaseServiceProviders();
         $this->registerCoreContainerAliases();
-
-        $this->bindPathsInContainer();
     }
 
     /**
@@ -161,22 +159,11 @@ class Application
         $this->register(new EventServiceProvider($this->container));
     }
 
-    /**
-     * Bind all of the application paths in the container.
-     *
-     * @return void
-     */
-    protected function bindPathsInContainer()
-    {
-        foreach (['base', 'public', 'storage', 'vendor'] as $path) {
-            $this->container->instance('path.'.$path, $this->paths->$path);
-        }
-    }
-
     /**
      * Get the base path of the Laravel installation.
      *
      * @return string
+     * @deprecated Will be removed in Beta.15.
      */
     public function basePath()
     {
@@ -187,6 +174,7 @@ class Application
      * Get the path to the public / web directory.
      *
      * @return string
+     * @deprecated Will be removed in Beta.15.
      */
     public function publicPath()
     {
@@ -197,6 +185,7 @@ class Application
      * Get the path to the storage directory.
      *
      * @return string
+     * @deprecated Will be removed in Beta.15.
      */
     public function storagePath()
     {
@@ -207,6 +196,7 @@ class Application
      * Get the path to the vendor directory where dependencies are installed.
      *
      * @return string
+     * @deprecated Will be removed in Beta.15.
      */
     public function vendorPath()
     {