Join with assignment: place the result at the assignment

#KT-21172 Fixed

idea/testData/intentions/joinDeclarationAndAssignment/atAssignment.kt.after

@@ -0,0 +1,8 @@
+fun test(repo: Repository, commitMessage: String) {
+    repo.git("add --verbose .")
+    val hash<selection>: String</selection><caret> = repo.git("commit -m $commitMessage")
+}
+
+class Repository {
+    fun git(s: String) = ""
+}