support multideclarations in Select Word

#KT-6833 Fixed

idea/testData/wordSelection/MultiDeclaration/0.kt

@@ -0,0 +1,3 @@
+fun f() {
+    val (a<caret>, b) = 1 to 2
+}

idea/testData/wordSelection/MultiDeclaration/1.kt

@@ -0,0 +1,3 @@
+fun f() {
+    val (<selection>a<caret></selection>, b) = 1 to 2
+}

idea/testData/wordSelection/MultiDeclaration/2.kt

@@ -0,0 +1,3 @@
+fun f() {
+    val (<selection>a<caret>, b</selection>) = 1 to 2
+}

idea/testData/wordSelection/MultiDeclaration/3.kt

@@ -0,0 +1,3 @@
+fun f() {
+    val <selection>(a<caret>, b)</selection> = 1 to 2
+}

idea/testData/wordSelection/MultiDeclaration/4.kt

@@ -0,0 +1,3 @@
+fun f() {
+    <selection>val (a<caret>, b) = 1 to 2</selection>
+}