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/Libraries/LibDiff/Format.cpp

@@ -8,14 +8,14 @@
 
 #include "Format.h"
 #include <AK/Assertions.h>
-#include <AK/DeprecatedString.h>
+#include <AK/ByteString.h>
 #include <AK/Stream.h>
 #include <AK/StringBuilder.h>
 #include <AK/Vector.h>
 #include <LibDiff/Hunks.h>
 
 namespace Diff {
-DeprecatedString generate_only_additions(StringView text)
+ByteString generate_only_additions(StringView text)
 {
     auto lines = text.split_view('\n', SplitBehavior::KeepEmpty);
     StringBuilder builder;
@@ -23,7 +23,7 @@ DeprecatedString generate_only_additions(StringView text)
     for (auto const& line : lines) {
         builder.appendff("+{}\n", line);
     }
-    return builder.to_deprecated_string();
+    return builder.to_byte_string();
 }
 
 ErrorOr<void> write_unified_header(StringView old_path, StringView new_path, Stream& stream)

Userland/Libraries/LibDiff/Format.h

@@ -13,7 +13,7 @@
 
 namespace Diff {
 
-DeprecatedString generate_only_additions(StringView);
+ByteString generate_only_additions(StringView);
 
 enum class ColorOutput {
     Yes,

Userland/Libraries/LibDiff/Hunks.cpp

@@ -65,7 +65,7 @@ ErrorOr<String> Parser::parse_file_line(Optional<size_t> const& strip_count)
 
     // No strip count given. Default to basename of file.
     if (!strip_count.has_value())
-        return String::from_deprecated_string(LexicalPath::basename(path));
+        return String::from_byte_string(LexicalPath::basename(path));
 
     // NOTE: We cannot use LexicalPath::parts as we want to strip the non-canonicalized path.
     auto const& parts = path.split_view('/');