Minor, capitalize language feature names in tests

To simplify textual search across the codebase

compiler/testData/diagnostics/ReadMe.md

@@ -60,11 +60,10 @@ The directive lets you compose a test consisting of several files in one actual
 ### 4. LANGUAGE
 
 This directive lets you enable or disable certain language features. Language features are named as
-parameters of the primary constructor of the class LanguageFeatureSettings. Each feature can be
-enabled with `+` or disabled with `-`.
+enum entries of the class LanguageFeature. Each feature can be enabled with `+` or disabled with `-`.
 
 #### Usage:
 
-    // !LANGUAGE: -topLevelSealedInheritance
+    // !LANGUAGE: -TopLevelSealedInheritance
 
-    // !LANGUAGE: +typeAliases -localDelegatedProperties
+    // !LANGUAGE: +TypeAliases -LocalDelegatedProperties

compiler/testData/diagnostics/tests/sourceCompatibility/noTopLevelSealedInheritance.kt

@@ -1,4 +1,4 @@
-// !LANGUAGE: -topLevelSealedInheritance
+// !LANGUAGE: -TopLevelSealedInheritance
 
 sealed class Base
 

compiler/tests/org/jetbrains/kotlin/checkers/BaseDiagnosticsTest.java

@@ -22,7 +22,6 @@ import com.intellij.lang.java.JavaLanguage;
 import com.intellij.openapi.util.Condition;
 import com.intellij.openapi.util.Conditions;
 import com.intellij.openapi.util.TextRange;
-import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.PsiFile;
 import com.intellij.psi.PsiFileFactory;
 import com.intellij.psi.search.GlobalSearchScope;
@@ -175,7 +174,7 @@ public abstract class BaseDiagnosticsTest
         do {
             boolean enable = matcher.group(1).equals("+");
             String name = matcher.group(2);
-            LanguageFeature feature = LanguageFeature.fromString(StringUtil.capitalize(name));
+            LanguageFeature feature = LanguageFeature.fromString(name);
             if (feature == null) {
                 Assert.fail(
                         "Language feature not found, please check spelling: " + name + "\n" +