Make the TaskLinterDSL warn by default

I am generally of the opinion that a linter should not abort progress by
default. I do, however, think that it should be on by default, making
warn a happy compromise.

main-settings/src/main/scala/sbt/dsl/LinterLevel.scala

@@ -40,29 +40,29 @@ package sbt.dsl
  *   }
  * }}}
  * To make this work, the instances are all defined as implicit case objects. Moreover, the
- * the [[LinterLevel.Abort]] setting is made default by placing [[LinterLevel.Warn]] and
+ * the [[LinterLevel.Warn]] setting is made default by placing [[LinterLevel.Abort]] and
  * [[LinterLevel.Ignore]] in the [[LinterLevelLowPriority]] trait that the [[LinterLevel]]
  * companion object extends.
  */
 sealed trait LinterLevel
 object LinterLevel extends LinterLevelLowPriority {
 
-  /**
-   * Abort the macro expansion if any linter check fails.
-   */
-  implicit case object Abort extends LinterLevel
-}
-
-private[dsl] trait LinterLevelLowPriority {
-
-  /**
-   * Do not perform any linting.
-   */
-  implicit case object Ignore extends LinterLevel
-
   /**
    * Apply the linter but print warnings instead of aborting macro expansion when linter violations
    * are found.
    */
   implicit case object Warn extends LinterLevel
 }
+
+private[dsl] trait LinterLevelLowPriority {
+
+  /**
+   * Abort the macro expansion if any linter check fails.
+   */
+  implicit case object Abort extends LinterLevel
+
+  /**
+   * Do not perform any linting.
+   */
+  implicit case object Ignore extends LinterLevel
+}

main-settings/src/test/scala/sbt/std/neg/TaskNegSpec.scala

@@ -39,6 +39,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -59,6 +60,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -78,6 +80,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -103,6 +106,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -132,6 +136,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -155,6 +160,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -176,6 +182,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -196,6 +203,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |var condition = true
@@ -215,6 +223,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |val barNeg = taskKey[String]("")
@@ -235,6 +244,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg = taskKey[String]("")
         |
@@ -252,6 +262,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg2 = taskKey[String]("")
         |
@@ -269,6 +280,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg2 = taskKey[String]("")
         |
@@ -289,6 +301,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg3 = taskKey[String]("")
         |def avoidDCE = {println(""); ""}
@@ -308,6 +321,7 @@ class TaskNegSpec extends FunSuite {
       """
         |import sbt._
         |import sbt.Def._
+        |import sbt.dsl.LinterLevel.Abort
         |
         |val fooNeg4 = taskKey[String]("")
         |