[lldb] Fix off-by-one error in ToDwarfSourceLanguage

The ToDwarfSourceLanguage function incorrectly excluded languages
that equal eLanguageTypeLastStandardLanguage. The comparison used
`<` instead of `<=`, causing the last standard language to fall
through to the default case and return std::nullopt.

This broke language plugins that use eLanguageTypeLastStandardLanguage
(currently Mojo at 0x0033) as their language code, preventing proper
DWARF language conversion and breaking REPL functionality.

The fix changes the comparison from `<` to `<=` to include the last
standard language in the automatic conversion to DWARF source language.

This is a regression from commit 7f51a2a
which introduced the ToDwarfSourceLanguage function.

Author: joshpeterson

lldb/source/Target/Language.cpp

@@ -549,7 +549,7 @@ Language::~Language() = default;
 
 static std::optional<llvm::dwarf::SourceLanguage>
 ToDwarfSourceLanguage(lldb::LanguageType language_type) {
-  if (language_type < lldb::eLanguageTypeLastStandardLanguage)
+  if (language_type <= lldb::eLanguageTypeLastStandardLanguage)
     return static_cast<llvm::dwarf::SourceLanguage>(language_type);
 
   switch (language_type) {