[lldb][Language] Add Language::GetDisplayNameForLanguageType API (llvm#161803)

The intention for this API is to be used when presenting language names
to the user, e.g., in expression evaluation diagnostics or LLDB errors.

Most uses of `GetNameForLanguageType` can be probably replaced with
`GetDisplayNameForLanguageType`, but that's out of scope of this PR.

This uses `llvm::dwarf::LanguageDescription` under the hood, so we would
lose the version numbers in the names. If we deem those to be important,
we could switch to an implementation that hardcodes a list of
user-friendly names with version numbers included.

The intention is to use it from
llvm#161688

Depends on llvm#161804

(cherry picked from commit 2c37244)

Author: Michael137

lldb/include/lldb/Target/Language.h

@@ -412,8 +412,15 @@ class Language : public PluginInterface {
   GetLanguageTypeFromString(const char *string) = delete;
   static lldb::LanguageType GetLanguageTypeFromString(llvm::StringRef string);
 
+  /// Returns the internal LLDB name for the specified language. When presenting
+  /// the language name to users, use \ref GetDisplayNameForLanguageType
+  /// instead.
   static const char *GetNameForLanguageType(lldb::LanguageType language);
 
+  /// Returns a user-friendly name for the specified language.
+  static llvm::StringRef
+  GetDisplayNameForLanguageType(lldb::LanguageType language);
+
   static void PrintAllLanguages(Stream &s, const char *prefix,
                                 const char *suffix);
 

lldb/source/Target/Language.cpp

@@ -272,6 +272,10 @@ const char *Language::GetNameForLanguageType(LanguageType language) {
     return language_names[eLanguageTypeUnknown].name;
 }
 
+llvm::StringRef Language::GetDisplayNameForLanguageType(LanguageType language) {
+  return SourceLanguage(language).GetDescription();
+}
+
 void Language::PrintSupportedLanguagesForExpressions(Stream &s,
                                                      llvm::StringRef prefix,
                                                      llvm::StringRef suffix) {