Everywhere: Rename {Deprecated => Byte}String

This commit un-deprecates DeprecatedString, and repurposes it as a byte
string.
As the null state has already been removed, there are no other
particularly hairy blockers in repurposing this type as a byte string
(what it _really_ is).

This commit is auto-generated:
  $ xs=$(ack -l \bDeprecatedString\b\|deprecated_string AK Userland \
    Meta Ports Ladybird Tests Kernel)
  $ perl -pie 's/\bDeprecatedString\b/ByteString/g;
    s/deprecated_string/byte_string/g' $xs
  $ clang-format --style=file -i \
    $(git diff --name-only | grep \.cpp\|\.h)
  $ gn format $(git ls-files '*.gn' '*.gni')

Userland/Applications/ThemeEditor/MainWidget.h

@@ -52,7 +52,7 @@ private:
     AlignmentModel() = default;
 
     struct AlignmentValue {
-        DeprecatedString title;
+        ByteString title;
         Gfx::TextAlignment setting_value;
     };
     Vector<AlignmentValue> m_alignments {
@@ -67,7 +67,7 @@ struct Property {
 };
 
 struct PropertyGroup {
-    DeprecatedString title;
+    ByteString title;
     Vector<Property> properties;
 };
 
@@ -96,7 +96,7 @@ private:
 
     void save_to_file(String const& filename, NonnullOwnPtr<Core::File> file);
     ErrorOr<Core::AnonymousBuffer> encode();
-    void set_path(DeprecatedString);
+    void set_path(ByteString);
 
     void build_override_controls();
 
@@ -105,7 +105,7 @@ private:
     void set_color(Gfx::ColorRole, Gfx::Color);
     void set_flag(Gfx::FlagRole, bool);
     void set_metric(Gfx::MetricRole, int);
-    void set_path(Gfx::PathRole, DeprecatedString);
+    void set_path(Gfx::PathRole, ByteString);
 
     void set_palette(Gfx::Palette);
 
@@ -123,7 +123,7 @@ private:
     RefPtr<GUI::Button> m_theme_override_apply;
     RefPtr<GUI::Button> m_theme_override_reset;
 
-    Optional<DeprecatedString> m_path;
+    Optional<ByteString> m_path;
     Gfx::Palette m_current_palette;
     MonotonicTime m_last_modified_time { MonotonicTime::now() };