Add Grails mail 4.0.0 plugin support. (#8)

* Add Grails mail 4.0.0 plugin support. Move AsynchronousMailService.groovy to src folder to save it from SendMail trait enrich.

* Fix failing test case due to metaclass methods access etc.

Author: vsachinv

README.md

@@ -25,6 +25,12 @@ Installation
 
 To install just add the plugin to the plugins block of `build.gradle`:
 
+For Grails 6.x.x
+```groovy
+implementation "io.github.gpc:asynchronous-mail:4.0.0-SNAPSHOT"
+```
+
+
 For Grails 5.x.x
 ```groovy
 implementation "io.github.gpc:asynchronous-mail:3.1.2"

build.gradle

@@ -35,7 +35,7 @@ dependencies {
     implementation 'org.grails.plugins:hibernate5'
     implementation 'org.hibernate:hibernate-core:5.6.15.Final'
     implementation 'org.grails.plugins:gsp'
-    implementation 'org.grails.plugins:mail:3.0.0'
+    implementation 'org.grails.plugins:mail:4.0.0'
     // This is needed for the quartz-plugin on grails >= 4.0.x, https://github.com/grails-plugins/grails-quartz/issues/107#issuecomment-575951471
     implementation('org.quartz-scheduler:quartz:2.3.2') { exclude group: 'slf4j-api', module: 'c3p0' }
     implementation 'org.grails.plugins:quartz:2.0.13'

src/main/groovy/grails/plugin/asyncmail/AsynchronousMailGrailsPlugin.groovy

@@ -13,13 +13,15 @@ import org.quartz.TriggerKey
 class AsynchronousMailGrailsPlugin extends Plugin {
 
     def grailsVersion = "6.0.0 > *"
+    def dependsOn = [mail: "* > 4.0.0"]
     def loadAfter = ['mail', 'quartz', 'hibernate', 'hibernate3', 'hibernate4', 'hibernate5', 'mongodb']
 
     @Override
     Closure doWithSpring() {
         { ->
             //noinspection GrUnresolvedAccess
             asynchronousMailMessageBuilderFactory(AsynchronousMailMessageBuilderFactory) { it.autowire = true }
+            asynchronousMailService(AsynchronousMailService) { it.autowire = true }
             //noinspection GrUnresolvedAccess
             springConfig.addAlias 'asyncMailService', 'asynchronousMailService'
         }

grails-app/services/grails/plugin/asyncmail/AsynchronousMailService.groovy renamed to src/main/groovy/grails/plugin/asyncmail/AsynchronousMailService.groovy

@@ -15,7 +15,7 @@ class CompareMessageBuilderSpec extends Specification {
 
         // Remove these methods as they are not part of MailMessageBuilder api and has found to be missing from
         // AsynchronousMailMessageBuilder with some versions of groovy which will make the test fail
-        mbMethods.removeAll { ['getProperty', 'setProperty', 'invokeMethod'].contains(it.name) }
+        mbMethods.removeAll { ['getProperty', 'setProperty', 'invokeMethod', 'access$0', 'pfaccess$0', 'pfaccess$1'].contains(it.name) }
 
         expect:
         mbMethods.every { MetaMethod mbm ->