PR #2102: guard size overflow in BytesToHexString and UrlEscape

Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/2102

BytesToHexString sizes its output as 2 * from.size() and UrlEscapeInternal as initial_portion + 3 * (input.size() - initial_portion), neither of which checks for a size_t overflow, so a large enough input wraps the length and StringResizeAndOverwrite allocates a buffer smaller than the number of bytes the following loop writes into it. CEscapedLength and CalculateBase64EscapedLenInternal in this same file already guard their expansions against size_t max with ABSL_INTERNAL_CHECK, so these two newer helpers just add the matching check with the appropriate divisor.
Merge d08c46485a00ab31af1ef8f06c2d9f7d4fa9d39e into 4890d3073b027fe5b5c541ca8d5b71daaecb2370

Merging this change closes #2102

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/2102 from nabhan06:escaping-size-overflow-guard d08c46485a00ab31af1ef8f06c2d9f7d4fa9d39e
PiperOrigin-RevId: 944523718
Change-Id: Ie10b04ed0f7f0aa0fc17aa33c028eba9cf7a0f61

absl/strings/escaping.cc

diff --git a/absl/strings/escaping.cc b/absl/strings/escaping.cc
index e9119ca..bdbc7ce 100644
--- a/absl/strings/escaping.cc
+++ b/absl/strings/escaping.cc
@@ -1177,6 +1177,8 @@
 
 std::string BytesToHexString(absl::string_view from) {
   std::string result;
+  ABSL_INTERNAL_CHECK(from.size() <= std::numeric_limits<size_t>::max() / 2,
+                      "BytesToHexString() overflow");
   StringResizeAndOverwrite(
       result, 2 * from.size(), [from](char* buf, size_t buf_size) {
         absl::BytesToHexStringInternal(
@@ -1211,6 +1213,10 @@
 
   // We need a buffer with enough space to store at most the initial portion
   // plus 3 bytes for each remaining character since escapes use 3 characters.
+  ABSL_INTERNAL_CHECK(
+      (input.size() - initial_portion) <=
+          (std::numeric_limits<size_t>::max() - initial_portion) / 3,
+      "UrlEscape() overflow");
   StringResizeAndOverwrite(
       output, initial_portion + 3 * (input.size() - initial_portion),
       [&](char* buf, size_t) {