Use mainClassName consistently across BootRun, BootJar, and BootWar

Previously, BootRun used the main property to configure the name of
the main class to run while BootJar and BootWar used the mainClass
property. Both were different to the application plugin which provides
a mainClassName project property.

This commit updates BootRun, BootJar, and BootWar to change the name
of the property used to configure the name of the main class to be
mainClassName. This makes the three Boot-specific tasks consistent
with each other, and also aligns them with Gradle's own application
plugin.

Closes gh-10622

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/packaging.adoc

@@ -85,7 +85,8 @@ By default, the executable archive's main class will be configured automatically
 looking for a class with a `public static void main(String[])` method in directories on
 the task's classpath.
 
-The main class can also be configured explicitly using the task's `mainClass` property:
+The main class can also be configured explicitly using the task's `mainClassName`
+property:
 
 [source,groovy,indent=0,subs="verbatim"]
 ----

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/running.adoc

@@ -11,8 +11,8 @@ To run your application without first building an archive use the `bootRun` task
 The `bootRun` task is automatically configured to use the runtime classpath of the
 main source set. By default, the main class will be discovered by looking for a class
 with a `public static void main(String[])` method in directories on the task's
-classpath. The main class can also be configured explicitly using the task's `main`
-property:
+classpath. The main class can also be configured explicitly using the task's
+`mainClassName` property:
 
 [source,groovy,indent=0,subs="verbatim"]
 ----

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-and-jar.gradle

@@ -20,5 +20,5 @@ bootJar {
 // end::classifier[]
 
 bootJar {
-	mainClass = 'com.example.Application'
+	mainClassName = 'com.example.Application'
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-custom-launch-script.gradle

@@ -8,7 +8,7 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'java'
 
 bootJar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 }
 
 // tag::custom-launch-script[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-include-launch-script.gradle

@@ -8,7 +8,7 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'java'
 
 bootJar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 }
 
 // tag::include-launch-script[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-launch-script-properties.gradle

@@ -8,7 +8,7 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'java'
 
 bootJar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 }
 
 // tag::launch-script-properties[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-main-class.gradle

@@ -9,6 +9,6 @@ apply plugin: 'java'
 
 // tag::main-class[]
 bootJar {
-	mainClass = 'com.example.ExampleApplication'
+	mainClassName = 'com.example.ExampleApplication'
 }
 // end::main-class[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-jar-requires-unpack.gradle

@@ -16,7 +16,7 @@ dependencies {
 }
 
 bootJar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 }
 
 // tag::requires-unpack[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-war-include-devtools.gradle

@@ -8,7 +8,7 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'war'
 
 bootWar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 	classpath file('spring-boot-devtools-1.2.3.RELEASE.jar')
 }
 

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/boot-war-properties-launcher.gradle

@@ -8,7 +8,7 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'war'
 
 bootWar {
-	mainClass 'com.example.ExampleApplication'
+	mainClassName 'com.example.ExampleApplication'
 }
 
 // tag::properties-launcher[]