Stop considering injected files as Kotlin source roots (KT-15032)

We should have a special facade for them as descriptors are not
present in ordinal project facade.

Caused by change in idea 171 (https://github.com/JetBrains/intellij-community/commit/b3527d9a20f4b9391e98b426beb2548fb3efc0fe)

 #KT-15032 Fixed

idea/testData/highlighter/KotlinInjection.kt

@@ -0,0 +1,6 @@
+package language_injection
+
+<info descr="null">import</info> org.intellij.lang.annotations.<info descr="null">Language</info>
+
+<info descr="null">@Language</info>("kotlin")
+val <info descr="null">test</info> = "<inject descr="null">fun test2() {}</inject>"