[idea] feat: set jvmTarget version explicitly (#2631)

feat(idea): set jvmTarget version explicitly

mirai-console/tools/intellij-plugin/resources/fileTemplates/code/Plugin build.gradle.ft

@@ -9,7 +9,11 @@ group = '$GROUP_ID'
 version = '$VERSION'
 
 repositories {
-    #if ($USE_PROXY_REPO) maven { url 'https://maven.aliyun.com/repository/public' } #end
+    #if($USE_PROXY_REPO)maven { url 'https://maven.aliyun.com/repository/public' }#end
 
     mavenCentral()
 }
+
+mirai {
+    jvmTarget JavaVersion.VERSION_1_8
+}

mirai-console/tools/intellij-plugin/resources/fileTemplates/code/Plugin build.gradle.kts.ft

@@ -10,7 +10,11 @@ group = "$GROUP_ID"
 version = "$VERSION"
 
 repositories {
-    #if ($USE_PROXY_REPO) maven("https://maven.aliyun.com/repository/public") #end
+    #if($USE_PROXY_REPO)maven("https://maven.aliyun.com/repository/public")#end
 
     mavenCentral()
 }
+
+mirai {
+    jvmTarget = JavaVersion.VERSION_1_8
+}