Update the Gradle plugins to the latest stable versions (#8312)

- https://plugins.gradle.org/plugin/org.jetbrains.intellij.platform
 - https://plugins.gradle.org/plugin/org.jetbrains.kotlin.jvm

This version bump of `org.jetbrains.intellij.platform` to `2.6.0` now
disallows the usage of powermocks, hence the deletion of the mocked
tests for the time being.

Author: jwren

build.gradle.kts

@@ -32,10 +32,11 @@ repositories {
 
 plugins {
   // https://plugins.jetbrains.com/docs/intellij/tools-intellij-platform-gradle-plugin.html
-  // https://github.com/JetBrains/intellij-platform-gradle-plugin/releases
+  // https://plugins.gradle.org/plugin/org.jetbrains.intellij.platform
   // https://plugins.gradle.org/plugin/org.jetbrains.kotlin.jvm
-  id("org.jetbrains.intellij.platform") version "2.5.0"
-  id("org.jetbrains.kotlin.jvm") version "2.1.21-RC2"
+  id("java") // Java support
+  id("org.jetbrains.intellij.platform") version "2.6.0" // IntelliJ Platform Gradle Plugin
+  id("org.jetbrains.kotlin.jvm") version "2.2.0" // Kotlin support
 }
 
 val flutterPluginVersion = providers.gradleProperty("flutterPluginVersion").get()
@@ -130,9 +131,6 @@ dependencies {
   // TODO(helin24): The rest in this block was pulled over from flutter-idea; potentially parts could be deleted.
   compileOnly("org.jetbrains:annotations:24.0.0")
   testImplementation("org.jetbrains:annotations:24.0.0")
-  testImplementation("org.powermock:powermock-api-mockito2:2.0.9")
-  testImplementation("org.powermock:powermock-module-junit4:2.0.9")
-  testImplementation(mapOf("group" to "org.mockito", "name" to "mockito-core", "version" to "5.2.0"))
 
   testRuntimeOnly(
     fileTree(