Rearrange build for docs

* Copy docs to the `$buildDir/reference` instead of `docs`
to make `asciidoctor` tasks to calculate their UP-TO-DATE key properly
* Generate `kdoc` outside the `docs` dir to not interfere with `asciidoctor`

Author: artembilan

build.gradle

@@ -565,7 +565,7 @@ project('spring-integration-core') {
     }
 
     dokkaHtmlPartial {
-        outputDirectory.set(new File(buildDir, 'docs/kdoc'))
+        outputDirectory.set(new File(buildDir, 'kdoc'))
         dokkaSourceSets {
             main {
                 sourceRoots.setFrom(file('src/main/kotlin'))
@@ -1164,7 +1164,7 @@ task api(type: Javadoc) {
 dokkaHtmlMultiModule {
     dependsOn api
     moduleName.set('spring-integration')
-    outputDirectory.set(file("$buildDir/docs/kdoc"))
+    outputDirectory.set(file("$buildDir/kdoc"))
 }
 
 apply from: "${rootDir}/gradle/docs.gradle"

gradle/docs.gradle

@@ -52,7 +52,7 @@ task checkAsciidocLinks {
 }
 
 def observationInputDir = file('spring-integration-core/src/main/java/org/springframework/integration/support/management/observation').absolutePath
-def generatedDocsDir = file("$buildDir/docs/generated").absolutePath
+def generatedDocsDir = file("$buildDir/reference/generated").absolutePath
 
 task generateObservabilityDocs(type: JavaExec) {
 	inputs.dir(observationInputDir)
@@ -74,7 +74,7 @@ task filterMetricsDocsContent(type: Copy) {
 task prepareDocs(type: Copy) {
 	dependsOn checkAsciidocLinks, filterMetricsDocsContent
 	from 'src/reference/asciidoc'
-	into "$buildDir/docs"
+	into "$buildDir/reference"
 }
 
 asciidoctorPdf {
@@ -88,8 +88,7 @@ asciidoctorPdf {
 	baseDirFollowsSourceFile()
 
 	asciidoctorj {
-		sourceDir "$buildDir/docs"
-		inputs.dir(sourceDir)
+		sourceDir "$buildDir/reference"
 		sources {
 			include 'index-single.adoc'
 		}
@@ -115,8 +114,7 @@ asciidoctor {
 	baseDirFollowsSourceFile()
 
 	configurations 'asciidoctorExtensions'
-	sourceDir "$buildDir/docs"
-	inputs.dir(sourceDir)
+	sourceDir "$buildDir/reference"
 	outputOptions {
 		backends 'spring-html'
 	}