LibSyntax: Add Language-from-String/Path functions

These are taken from HackStudio, but slightly rearranged to be more
alphabetical, and returning an empty Optional instead of "Unknown".

Userland/Libraries/LibSyntax/Language.cpp

@@ -5,6 +5,7 @@
  */
 
 #include "Language.h"
+#include <AK/LexicalPath.h>
 #include <LibGUI/TextEditor.h>
 #include <LibSyntax/Highlighter.h>
 
@@ -72,4 +73,69 @@ StringView common_language_extension(Language language)
     VERIFY_NOT_REACHED();
 }
 
+Optional<Language> language_from_name(StringView name)
+{
+    if (name.equals_ignoring_ascii_case("CMake"sv))
+        return Language::CMake;
+    if (name.equals_ignoring_ascii_case("CMakeCache"sv))
+        return Language::CMakeCache;
+    if (name.equals_ignoring_ascii_case("Cpp"sv))
+        return Language::Cpp;
+    if (name.equals_ignoring_ascii_case("CSS"sv))
+        return Language::CSS;
+    if (name.equals_ignoring_ascii_case("GitCommit"sv))
+        return Language::GitCommit;
+    if (name.equals_ignoring_ascii_case("GML"sv))
+        return Language::GML;
+    if (name.equals_ignoring_ascii_case("HTML"sv))
+        return Language::HTML;
+    if (name.equals_ignoring_ascii_case("INI"sv))
+        return Language::INI;
+    if (name.equals_ignoring_ascii_case("JavaScript"sv))
+        return Language::JavaScript;
+    if (name.equals_ignoring_ascii_case("PlainText"sv))
+        return Language::PlainText;
+    if (name.equals_ignoring_ascii_case("SQL"sv))
+        return Language::SQL;
+    if (name.equals_ignoring_ascii_case("Shell"sv))
+        return Language::Shell;
+
+    return {};
+}
+
+Optional<Language> language_from_filename(LexicalPath const& file)
+{
+    if (file.title() == "COMMIT_EDITMSG"sv)
+        return Language::GitCommit;
+
+    auto extension = file.extension();
+    VERIFY(!extension.starts_with('.'));
+    if (extension == "cmake"sv || (extension == "txt"sv && file.title() == "CMakeLists"sv))
+        return Language::CMake;
+    if (extension == "txt"sv && file.title() == "CMakeCache"sv)
+        return Language::CMakeCache;
+    if (extension.is_one_of("c"sv, "cc"sv, "cxx"sv, "cpp"sv, "c++", "h"sv, "hh"sv, "hxx"sv, "hpp"sv, "h++"sv))
+        return Language::Cpp;
+    if (extension == "css"sv)
+        return Language::CSS;
+    if (extension == "gml"sv)
+        return Language::GML;
+    if (extension.is_one_of("html"sv, "htm"sv))
+        return Language::HTML;
+    if (extension.is_one_of("ini"sv, "af"sv))
+        return Language::INI;
+    if (extension.is_one_of("js"sv, "mjs"sv, "json"sv))
+        return Language::JavaScript;
+    if (extension.is_one_of("sh"sv, "bash"sv))
+        return Language::Shell;
+    if (extension == "sql"sv)
+        return Language::SQL;
+
+    // Check "txt" after the CMake related files that use "txt" as their extension.
+    if (extension == "txt"sv)
+        return Language::PlainText;
+
+    return {};
+}
+
 }

Userland/Libraries/LibSyntax/Language.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Forward.h>
 #include <AK/StringView.h>
 
 namespace Syntax {
@@ -27,5 +28,7 @@ enum class Language {
 
 StringView language_to_string(Language);
 StringView common_language_extension(Language);
+Optional<Language> language_from_name(StringView);
+Optional<Language> language_from_filename(LexicalPath const&);
 
 }