weston: add more libinput config options

This is so that, for instance, people using weston as their main Wayland
compositor can invert the sense of two finger scrolling or change
pointer acceleration using weston.ini, rather than having to edit C
code.

All of the options that libinput itself exposes through its API are now
exposed in weston.ini.  The new options are called `tap-and-drag`,
`tap-and-drag-lock`, `disable-while-typing`, `middle-emulation`,
`left-handed`, `rotation`, `accel-profile`, `accel-speed`,
`scroll-method`, `natural-scroll`, and `scroll-button`. I have
successfully tested everything except for `rotation`, out of a lack of
hardware support.

weston now depends directly on libevdev for turning button name strings into
kernel input codes. This was needed for the `scroll-button` config
option. (weston already depends indirectly on libevdev through
libinput, so I figured people would be OK with this.) As a practical
matter for debian-style packagers, weston now has a build dependency on
libevdev-dev.

Right now, the code applies the same options to all attached devices
that a given option is relevant for. There are plans for multiple
[libinput] sections, each with different device filters, for users who
need more control here.

Signed-off-by: Eric Toombs <3672-ewtoombs@users.noreply.gitlab.freedesktop.org>

man/weston.ini.man

@@ -212,12 +212,80 @@ There is also a command line option to do the same.
 The
 .B libinput
 section is used to configure input devices when using the libinput input device
-backend.
+backend. The defaults are determined by libinput and vary according to what is
+most sensible for any given device.
 .PP
 Available configuration are:
 .TP 7
-.BI "enable-tap=" true
-enables tap to click on touchpad devices
+.BI "enable-tap=" false
+Enables tap to click on touchpad devices.
+.TP 7
+.BI "tap-and-drag=" false
+For touchpad devices with \fBenable-tap\fR enabled. If the user taps, then
+taps a second time, this time holding, the virtual mouse button stays down for
+as long as the user keeps their finger on the touchpad, allowing the user to
+click and drag with taps alone.
+.TP 7
+.BI "tap-and-drag-lock=" false
+For touchpad devices with \fBenable-tap\fR and \fBtap-and-drag\fR enabled.
+In the middle of a tap-and-drag, if the user releases the touchpad for less
+than a certain number of milliseconds, then touches it again, the virtual mouse
+button will remain pressed and the drag can continue.
+.TP 7
+.BI "disable-while-typing=" true
+For devices that may be accidentally triggered while typing on the keyboard,
+causing a disruption of the typing.  Disables them while the keyboard is in
+use.
+.TP 7
+.BI "middle-button-emulation=" false
+For pointer devices with left and right buttons, but no middle button.  When
+enabled, a middle button event is emitted when the left and right buttons are
+pressed simultaneously.
+.TP 7
+.BI "left-handed=" false
+Configures the device for use by left-handed people. Exactly what this option
+does depends on the device. For pointers with left and right buttons, the
+buttons are swapped. On tablets, the tablet is logically turned upside down,
+because it will be physically turned upside down.
+.TP 7
+.BI "rotation=" n
+Changes the direction of the logical north, rotating it \fIn\fR degrees
+clockwise away from the default orientation, where \fIn\fR is a whole
+number between 0 and 359 inclusive. Needed for trackballs, mainly. Allows the
+user to orient the trackball sideways, for example.
+.TP 7
+.BI "accel-profile=" "{flat,adaptive}"
+Set the pointer acceleration profile. The pointer's screen speed is
+proportional to the physical speed with a certain constant of proportionality.
+Call that constant alpha. \fIflat\fR keeps alpha fixed. See \fBaccel-speed\fR.
+\fIadaptive\fR causes alpha to increase with physical speed, giving the user
+more control when the speed is slow, and more reach when the speed is high.
+\fIadaptive\fR is the default.
+.TP 7
+.BI "accel-speed=" v
+If \fBaccel-profile\fR is set to \fIflat\fR, it simply sets the value of alpha.
+If \fBaccel-profile\fR is set to \fIadaptive\fR, the effect is more
+complicated, but generally speaking, it will change the pointer's speed.
+\fIv\fR is normalised and must lie in the range [-1, 1]. The exact mapping
+between \fIv\fR and alpha is hardware-dependent, but higher values cause higher
+cursor speeds.
+.TP 7
+.BI "natural-scroll=" false
+Enables natural scrolling, mimicking the behaviour of touchscreen scrolling.
+That is, if the wheel, finger, or fingers are moved down, the surface is
+scrolled up instead of down, as if the finger, or fingers were in contact with
+the surface being scrolled.
+.TP 7
+.BI "scroll-method=" {two-finger,edge,button,none}
+Sets the scroll method. \fItwo-finger\fR scrolls with two fingers on a
+touchpad. \fIedge\fR scrolls with one finger on the right edge of a touchpad.
+\fIbutton\fR scrolls when the pointer is moved while a certain button is
+pressed. See \fBscroll-button\fR. \fInone\fR disables scrolling altogether.
+.TP 7
+.BI "scroll-button=" {BTN_LEFT,BTN_RIGHT,BTN_MIDDLE,...}
+For devices with \fBscroll-method\fR set to \fIbutton\fR. Specifies the
+button that will trigger scrolling. See /usr/include/linux/input-event-codes.h
+for the complete list of possible values.
 .TP 7
 .BI "touchscreen_calibrator=" true
 Advertise the touchscreen calibrator interface to all clients. This is a