Make joystick platform code init on demand

This makes joystick support initialize the first time a joystick
function is called, including those gamepad functions that are layered
on top of joystick functions.

Related to #1284.
Related to #1646.

docs/input.dox

@@ -550,10 +550,10 @@ int present = glfwJoystickPresent(GLFW_JOYSTICK_1);
 Each joystick has zero or more axes, zero or more buttons, zero or more hats,
 a human-readable name, a user pointer and an SDL compatible GUID.
 
-When GLFW is initialized, detected joysticks are added to the beginning of
-the array.  Once a joystick is detected, it keeps its assigned ID until it is
-disconnected or the library is terminated, so as joysticks are connected and
-disconnected, there may appear gaps in the IDs.
+Detected joysticks are added to the beginning of the array.  Once a joystick is
+detected, it keeps its assigned ID until it is disconnected or the library is
+terminated, so as joysticks are connected and disconnected, there may appear
+gaps in the IDs.
 
 Joystick axis, button and hat state is updated when polled and does not require
 a window to be created or events to be processed.  However, if you want joystick

docs/intro.dox

@@ -22,8 +22,8 @@ There are also guides for the other areas of GLFW.
 
 Before most GLFW functions may be called, the library must be initialized.
 This initialization checks what features are available on the machine,
-enumerates monitors and joysticks, initializes the timer and performs any
-required platform-specific initialization.
+enumerates monitors, initializes the timer and performs any required
+platform-specific initialization.
 
 Only the following functions may be called before the library has been
 successfully initialized, and only from the main thread.

docs/news.dox

@@ -55,6 +55,21 @@ applications.
 
 @subsection caveats_34 Caveats for version 3.4
 
+@subsubsection joysticks_34 Joystick support is initialized on demand
+
+The joystick part of GLFW is now initialized when first used, primarily to work
+around faulty Windows drivers that cause DirectInput to take up to several
+seconds to enumerate devices.
+
+This change will usually not be observable.  However, if your application waits
+for events without having first called any joystick function or created any
+visible windows, the wait may never unblock as GLFW may not yet have subscribed
+to joystick related OS events.
+
+To work around this, call any joystick function before waiting for events, for
+example by setting a [joystick callback](@ref joystick_event).
+
+
 @subsubsection standalone_34 Tests and examples are disabled when built as a sub-project
 
 GLFW now does not build the tests and examples when it is added as