Add CandidateForRemoval annotation

Author: koperagen

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/annotations/CandidateForRemoval.kt

@@ -0,0 +1,9 @@
+package org.jetbrains.kotlinx.dataframe.annotations
+
+/**
+ * Functions that can be replaced with other API, such as shortcuts without clean value,
+ * or something not properly designed, and so will be considered to be removed from API.
+ * If you see a function marked with it and think it should be kept, please let us know in the GitHub issue:
+ * https://github.com/Kotlin/dataframe/issues/1028
+ */
+internal annotation class CandidateForRemoval