Stabilize UI Test library for Desktop (#3518)

For iOS/Web it will be stabilized with stabilizing these targets themselves. Also, we should expose uiTest for them, not uiTestJUnit4

JUnit5 support will be provided in the future in [this issue](https://github.com/JetBrains/compose-multiplatform/issues/2371)

## API Changes

- Testing framework is stabilized for Desktop
- `compose.uiTestJUnit4` is renamed to `compose.desktop.uiTestJUnit4`

gradle-plugins/compose/src/main/kotlin/org/jetbrains/compose/ComposePlugin.kt

@@ -106,6 +106,7 @@ abstract class ComposePlugin : Plugin<Project> {
         val runtime get() = composeDependency("org.jetbrains.compose.runtime:runtime")
         val runtimeSaveable get() = composeDependency("org.jetbrains.compose.runtime:runtime-saveable")
         val ui get() = composeDependency("org.jetbrains.compose.ui:ui")
+        @Deprecated("Use desktop.uiTestJUnit4", replaceWith = ReplaceWith("desktop.uiTestJUnit4"))
         @ExperimentalComposeLibrary
         val uiTestJUnit4 get() = composeDependency("org.jetbrains.compose.ui:ui-test-junit4")
         val uiTooling get() = composeDependency("org.jetbrains.compose.ui:ui-tooling")
@@ -127,6 +128,8 @@ abstract class ComposePlugin : Plugin<Project> {
         val macos_x64 = composeDependency("org.jetbrains.compose.desktop:desktop-jvm-macos-x64")
         val macos_arm64 = composeDependency("org.jetbrains.compose.desktop:desktop-jvm-macos-arm64")
 
+        val uiTestJUnit4 get() = composeDependency("org.jetbrains.compose.ui:ui-test-junit4")
+
         val currentOs by lazy {
             composeDependency("org.jetbrains.compose.desktop:desktop-jvm-${currentTarget.id}")
         }