Configure issue/PR URLs in IntelliJ via Gradle (#229 / #262)

Configure Gradle to configure IntelliJ to link issue and PR numbers
to GitHub. This is implemented with a build.gradle file because we
found it easier to manipulate XML with. A rewrite in Kotlin should
be evaluated in the future.

Closes: #229
PR: #262

build.gradle.kts

@@ -3,7 +3,7 @@ plugins {
     jacoco
     checkstyle
     `maven-publish`
-    id("com.diffplug.gradle.spotless") version "3.27.1"
+    id("com.diffplug.gradle.spotless") version "4.0.0"
     id("org.shipkit.java") version "2.3.1"
     id("at.zierler.yamlvalidator") version "1.5.0"
     id("org.sonarqube") version "2.8"

buildSrc/build.gradle

@@ -0,0 +1,27 @@
+import groovy.xml.XmlUtil
+
+build {
+    doLast {
+        def ideaFolder = new File('.idea');
+        if(ideaFolder.exists() && ideaFolder.isDirectory()) {
+            def xmlFile = new File(".idea/vcs.xml")
+            def xml = new XmlSlurper().parse(xmlFile)
+            xml.component.find {it.@name == 'IssueNavigationConfiguration'}.replaceNode {}
+            xml.appendNode {
+                component(name: "IssueNavigationConfiguration") {
+                    option(name: 'links') {
+                        list {
+                            IssueNavigationLink {
+                                option(name: "issueRegexp", value: '#(\\d+)')
+                                option(name: "linkRegexp", value: 'https://github.com/junit-pioneer/junit-pioneer/issues/$1')
+                            }
+                        }
+                    }
+                }
+            }
+            xmlFile.withWriter {out->
+                XmlUtil.serialize(xml, out)
+            }
+        }
+    }
+}