Factor default Ivy pattern

cache/src/main/scala/coursier/Cache.scala

@@ -746,9 +746,7 @@ object Cache {
   }
 
   lazy val ivy2Local = IvyRepository(
-    ivy2HomeUri + "local/" +
-      "[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/" +
-      "[artifact](-[classifier]).[ext]",
+    ivy2HomeUri + "local/" + coursier.ivy.Pattern.default,
     dropInfoAttributes = true
   )
 

core/shared/src/main/scala/coursier/ivy/Pattern.scala

@@ -9,6 +9,10 @@ import java.util.regex.Pattern.quote
 
 object Pattern {
 
+  val default =
+    "[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/" +
+    "[artifact](-[classifier]).[ext]"
+
   val propertyRegex = (quote("${") + "[^" + quote("{[()]}") + "]*" + quote("}")).r
   val optionalPartRegex = (quote("(") + "[^" + quote("{()}") + "]*" + quote(")")).r
   val variableRegex = (quote("[") + "[^" + quote("{[()]}") + "]*" + quote("]")).r