Language version 2.0: fix compiler messages and minor details

compiler/testData/cli/jvm/firHello.out

@@ -1,3 +1,3 @@
-warning: compiler flag -Xuse-k2 is deprecated, please use -language-version 2.0 instead
+warning: compiler flag -Xuse-k2 is deprecated, please use "-language-version 2.0" instead
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
 OK

compiler/testData/cli/jvm/firHello20WithFlag.out

@@ -1,3 +1,3 @@
-warning: compiler flag -Xuse-k2 is redundant
+warning: compiler flag -Xuse-k2 is redundant, the "-language-version 2.0" is used instead
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
 OK

compiler/testData/cli/jvm/firHello20WithOldLV.out

@@ -1,3 +1,3 @@
-warning: with -Xuse-k2 compiler flag -language-version 1.5 has no effect, please remove -Xuse-k2 flag or use -language-version 2.0 instead
+warning: with -Xuse-k2 compiler flag "-language-version 1.5" has no effect, please remove -Xuse-k2 flag and use "-language-version 2.0" instead
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
 OK

compiler/testData/cli/metadata/fir.out

@@ -1,3 +1,3 @@
 warning: language version 2.0 is experimental, there are no backwards compatibility guarantees for new language and library features
-error: compilation to metadata is not supported in language version 2.0 right now
+error: compilation to metadata is not supported with language version 2.0 right now
 COMPILATION_ERROR