middleclick-autoscroll 1.0.0

Middle-click autoscroll for every Chromium-based application on the system:
Electron and CEF applications, Chromium-based browsers, Flatpaks, Spotify and
Steam, plus anything installed later.

The flag goes into an Arch wrapper's <name>-flags.conf where one exists, and
into a shadowing desktop entry where it does not. Steam gets its web helper
script patched and -noverifyfiles on its launcher, because it restores its own
files otherwise. Every change is recorded so it can be taken back exactly.

res/systemd/middleclick-autoscroll.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=Apply middle-click autoscroll to Chromium-based applications
+Documentation=man:middleclick-autoscroll(1)
+
+[Service]
+Type=oneshot
+ExecStart=@BINDIR@/middleclick-autoscroll apply --quiet
+# Scanning binaries for their engine is the slow part, and it is cached; a run
+# that takes longer than this has found something pathological and should not
+# be left running at every login.
+TimeoutStartSec=180
+Nice=10
+IOSchedulingClass=idle
+
+[Install]
+WantedBy=default.target