Minor: get line start without whitespaces in KotlinExtraVariablesProvider

#KT-10183 Fxied

idea/testData/debugger/tinyApp/src/evaluate/singleBreakpoint/extraVariables/evFunctionDeclaration.kt

@@ -0,0 +1,12 @@
+package evFunctionDeclaration
+
+class A(val a: Int) {
+    //Breakpoint!
+    fun foo() = a
+}
+
+fun main(args: Array<String>) {
+    A(1).foo()
+}
+
+// PRINT_FRAME