basename: Support suffix stripping

Allow passing an optional suffix argument to `basename` which is then
stripped from the resulting basename (unless the resulting basename is
identical to the suffix.)

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/basename.html

Userland/Utilities/basename.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,12 +16,18 @@ int main(int argc, char** argv)
         return 1;
     }
 
-    const char* path = nullptr;
+    StringView path;
+    StringView suffix;
 
     Core::ArgsParser args_parser;
     args_parser.add_positional_argument(path, "Path to get basename from", "path");
+    args_parser.add_positional_argument(suffix, "Suffix to strip from name", "suffix", Core::ArgsParser::Required::No);
     args_parser.parse(argc, argv);
 
-    printf("%s\n", LexicalPath(path).basename().characters());
+    auto basename = LexicalPath(path).basename();
+    if (!suffix.is_null() && basename.length() != suffix.length() && basename.ends_with(suffix))
+        outln("{}", basename.substring_view(0, basename.length() - suffix.length()));
+    else
+        outln("{}", basename);
     return 0;
 }