Register CC's modems as brittle

This tells Create that modems will pop-off if their neighbour is moved,
and so changes the order that the block is moved in.

We possibly should use BlockMovementChecks.AttachedCheck instead, to
properly handle the direction modems are facing in. However, this
doesn't appear to be part of the public API, so probably best avoided.

Fixes #948

projects/forge/src/generated/resources/data/create/tags/blocks/brittle.json

@@ -0,0 +1,3 @@
+{
+  "values": ["computercraft:cable", "computercraft:wireless_modem_advanced", "computercraft:wireless_modem_advanced"]
+}