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')

Tests/AK/TestStack.cpp

@@ -26,7 +26,7 @@ TEST_CASE(basic)
 
 TEST_CASE(complex_type)
 {
-    AK::Stack<DeprecatedString, 4> stack;
+    AK::Stack<ByteString, 4> stack;
 
     EXPECT_EQ(stack.is_empty(), true);
     EXPECT(stack.push("Well"));