Rename CharSequence.get to charAt

This is done for JVM interoperability. There's still a member function
String.get() and an extension function "get" on CharSequence

 #KT-1730 Fixed
 #KT-5389 Fixed

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -6294,6 +6294,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("kt1730_implementCharSequence.kt")
+            public void testKt1730_implementCharSequence() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/j+k/kt1730_implementCharSequence.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("kt2152.kt")
             public void testKt2152() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/j+k/kt2152.kt");

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxWithStdlibCodegenTestGenerated.java

@@ -2832,6 +2832,12 @@ public class BlackBoxWithStdlibCodegenTestGenerated extends AbstractBlackBoxCode
             doTestWithStdlib(fileName);
         }
 
+        @TestMetadata("kt5389_stringBuilderGet.kt")
+        public void testKt5389_stringBuilderGet() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/boxWithStdlib/strings/kt5389_stringBuilderGet.kt");
+            doTestWithStdlib(fileName);
+        }
+
         @TestMetadata("stringPlusOnlyWorksOnString.kt")
         public void testStringPlusOnlyWorksOnString() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/boxWithStdlib/strings/stringPlusOnlyWorksOnString.kt");