Consistenty use javax annotations. (#1197)

- Unfortunately jetbrains annotations seem to be exposed transitively via core somewhere, but with the correct IDE settings, annotations can be defaulted to javax
 - Cleaning up of import order in #1195
 - Must be merged before #1195

Co-authored-by: NotMyFault <mc.cache@web.de>

buildSrc/src/main/kotlin/PlatformConfig.kt

@@ -55,7 +55,6 @@ fun Project.applyPlatformAndCoreConfiguration() {
     }
 
     dependencies {
-        "compileOnly"("org.jetbrains:annotations:20.1.0")
         "testImplementation"("org.junit.jupiter:junit-jupiter-api:${Versions.JUNIT}")
         "testImplementation"("org.junit.jupiter:junit-jupiter-params:${Versions.JUNIT}")
         "testImplementation"("org.mockito:mockito-core:${Versions.MOCKITO}")