Make CharSequence.length a function instead of property

And String.length as well.

This is done for JVM interoperability: java.lang.CharSequence is an open class
and has a function 'length()' which should be implemented in subclasses
somehow.

A minor unexpected effect of this is that String.length() is now a compile-time
constant (it wasn't such as a property because properties are not supported in
compile-time constant evaluation)

 #KT-3571 Fixed

compiler/testData/codegen/boxAgainstJava/sam/adapters/severalSamParameters.kt

@@ -1,6 +1,6 @@
 fun box(): String {
     var v = "FAIL"
-    val max = JavaClass.findMaxAndInvokeCallback({ a, b -> a.length - b.length }, "foo", "kotlin", { v = "OK" })
+    val max = JavaClass.findMaxAndInvokeCallback({ a, b -> a.length() - b.length() }, "foo", "kotlin", { v = "OK" })
     if (max != "kotlin") return "Wrong max: $max"
     return v
-}
+}

compiler/testData/codegen/boxAgainstJava/sam/adapters/typeParameterOfClass.kt

@@ -1,6 +1,6 @@
 fun box(): String {
     val wc = WeirdComparator<String>()
-    val result = wc.max({ a, b -> a.length - b.length }, "java", "kotlin")
+    val result = wc.max({ a, b -> a.length() - b.length() }, "java", "kotlin")
     if (result != "kotlin") return "Wrong: $result"
     return "OK"
-}
+}

compiler/testData/codegen/boxAgainstJava/sam/adapters/typeParameterOfMethod.kt

@@ -1,9 +1,9 @@
 fun box(): String {
-    val result = WeirdComparator.max<String>({ a, b -> a.length - b.length }, "java", "kotlin")
+    val result = WeirdComparator.max<String>({ a, b -> a.length() - b.length() }, "java", "kotlin")
     if (result != "kotlin") return "Wrong: $result"
 
-    val result2 = WeirdComparator.max2<String>({ a, b -> a.length - b.length }, "java", "kotlin")
+    val result2 = WeirdComparator.max2<String>({ a, b -> a.length() - b.length() }, "java", "kotlin")
     if (result2 != "kotlin") return "Wrong: $result"
 
     return "OK"
-}
+}

compiler/testData/codegen/boxAgainstJava/sam/adapters/typeParameterOfOuterClass.kt

@@ -1,6 +1,6 @@
 fun box(): String {
     val wc = WeirdComparator<String>().createInner()!!
-    val result = wc.max({ a, b -> a.length - b.length }, "java", "kotlin")
+    val result = wc.max({ a, b -> a.length() - b.length() }, "java", "kotlin")
     if (result != "kotlin") return "Wrong: $result"
     return "OK"
 }