Fixed #1799 by creating a separate intellijPlatformComposedJarApi (extends api & compileOnlyApi) configuration with JAVA_API usage attribute value. Also replaced java plugin by java-library plugin, because it is a more proper plugin for IntelliJ plugin projects (they are libraries).

Fixed #1799 by creating a separate intellijPlatformComposedJarApi (extends api & compileOnlyApi) configuration with JAVA_API usage attribute value. Also replaced java plugin by java-library plugin, because it is a more proper plugin for IntelliJ plugin projects (they are libraries). #2821