Register modems as attached to their adjacent block

In c8eadf4011 we marked our various modems
as "brittle", which ensures they do not pop-off computers when the whole
structure moves.

However, this still requires the modem to be glued — if the modem is
outside the superglue range, it will still pop off. We can fix it by
registering a special "attached check" for the various modem blocks,
which says that the modem should be moved when the adjacent block does.

Fixes #1913

buildSrc/src/main/kotlin/cc-tweaked.java-convention.gradle.kts

@@ -54,6 +54,7 @@ repositories {
         filter {
             includeGroup("cc.tweaked")
             // Things we mirror
+            includeGroup("com.simibubi.create")
             includeGroup("commoble.morered")
             includeGroup("dev.architectury")
             includeGroup("dev.emi")