AK: Add String::find_last() and inline String::find() methods

This adds the String::find_last() as wrapper for StringUtils::find_last,
which is another step in harmonizing the String and StringView APIs
where possible.

This also inlines the find() methods, as they are simple wrappers around
StringUtils functions without any additional logic.

AK/String.cpp

@@ -459,14 +459,4 @@ String String::vformatted(StringView fmtstr, TypeErasedFormatParams params)
     return builder.to_string();
 }
 
-Optional<size_t> String::find(char c, size_t start) const
-{
-    return find(StringView { &c, 1 }, start);
-}
-
-Optional<size_t> String::find(StringView const& view, size_t start) const
-{
-    return StringUtils::find(*this, view, start);
-}
-
 }

AK/String.h

@@ -141,8 +141,10 @@ public:
     [[nodiscard]] Vector<String> split_limit(char separator, size_t limit, bool keep_empty = false) const;
     [[nodiscard]] Vector<String> split(char separator, bool keep_empty = false) const;
 
-    [[nodiscard]] Optional<size_t> find(char, size_t start = 0) const;
-    [[nodiscard]] Optional<size_t> find(StringView const&, size_t start = 0) const;
+    [[nodiscard]] Optional<size_t> find(char needle, size_t start = 0) const { return StringUtils::find(*this, needle, start); }
+    [[nodiscard]] Optional<size_t> find(StringView const& needle, size_t start = 0) const { return StringUtils::find(*this, needle, start); }
+    [[nodiscard]] Optional<size_t> find_last(char needle) const { return StringUtils::find_last(*this, needle); }
+    // FIXME: Implement find_last(StringView const&) for API symmetry.
     [[nodiscard]] Vector<size_t> find_all(StringView const& needle) const { return StringUtils::find_all(*this, needle); }
 
     [[nodiscard]] String substring(size_t start) const;