AK: Add case-insensitive hashing for the new String classes

Bringing over this functionality from DeprecatedString.

Author: awesomekling

AK/FlyString.cpp

@@ -100,6 +100,11 @@ unsigned FlyString::hash() const
     return String::fly_string_data_to_hash({}, m_data);
 }
 
+u32 FlyString::ascii_case_insensitive_hash() const
+{
+    return case_insensitive_string_hash(reinterpret_cast<char const*>(bytes().data()), bytes().size());
+}
+
 FlyString::operator String() const
 {
     return to_string();

AK/FlyString.h

@@ -36,6 +36,7 @@ class FlyString {
 
     [[nodiscard]] bool is_empty() const;
     [[nodiscard]] unsigned hash() const;
+    [[nodiscard]] u32 ascii_case_insensitive_hash() const;
 
     explicit operator String() const;
     String to_string() const;
@@ -88,6 +89,11 @@ struct Formatter<FlyString> : Formatter<StringView> {
     ErrorOr<void> format(FormatBuilder&, FlyString const&);
 };
 
+struct ASCIICaseInsensitiveFlyStringTraits : public Traits<String> {
+    static unsigned hash(FlyString const& s) { return s.ascii_case_insensitive_hash(); }
+    static bool equals(FlyString const& a, FlyString const& b) { return a.bytes().data() == b.bytes().data() || a.bytes_as_string_view().equals_ignoring_ascii_case(b.bytes_as_string_view()); }
+};
+
 }
 
 [[nodiscard]] ALWAYS_INLINE AK::FlyString operator""_fly_string(char const* cstring, size_t length)

AK/String.cpp

@@ -439,6 +439,11 @@ u32 String::hash() const
     return m_data->hash();
 }
 
+u32 String::ascii_case_insensitive_hash() const
+{
+    return case_insensitive_string_hash(reinterpret_cast<char const*>(bytes().data()), bytes().size());
+}
+
 Utf8View String::code_points() const
 {
     return Utf8View(bytes_as_string_view());

AK/String.h

@@ -168,6 +168,7 @@ class String {
     [[nodiscard]] bool contains(u32, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
 
     [[nodiscard]] u32 hash() const;
+    [[nodiscard]] u32 ascii_case_insensitive_hash() const;
 
     template<Arithmetic T>
     static ErrorOr<String> number(T value)
@@ -263,6 +264,11 @@ struct Formatter<String> : Formatter<StringView> {
     ErrorOr<void> format(FormatBuilder&, String const&);
 };
 
+struct ASCIICaseInsensitiveStringTraits : public Traits<String> {
+    static unsigned hash(String const& s) { return s.ascii_case_insensitive_hash(); }
+    static bool equals(String const& a, String const& b) { return a.bytes_as_string_view().equals_ignoring_ascii_case(b.bytes_as_string_view()); }
+};
+
 }
 
 [[nodiscard]] ALWAYS_INLINE AK::String operator""_string(char const* cstring, size_t length)