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/TestBinaryHeap.cpp

@@ -7,7 +7,7 @@
 #include <LibTest/TestCase.h>
 
 #include <AK/BinaryHeap.h>
-#include <AK/DeprecatedString.h>
+#include <AK/ByteString.h>
 
 using namespace Test::Randomized;
 
@@ -46,7 +46,7 @@ TEST_CASE(populate_int)
 
 TEST_CASE(populate_string)
 {
-    BinaryHeap<int, DeprecatedString, 5> strings;
+    BinaryHeap<int, ByteString, 5> strings;
     strings.insert(1, "ABC");
     strings.insert(2, "DEF");
     EXPECT_EQ(strings.size(), 2u);