GH-49973: [C++] Fix Gandiva string length checks

[puneetdixit200]

Rationale

Fixes remaining Gandiva string length safety issues from GH-49973.

What changed

• Uses checked multiplication before addition in quote_utf8 and to_hex_binary.
• Rejects negative valid input lengths in concat_ws before allocation/copy.
• Adds targeted regression tests for overflow and negative length handling.

Verification

• git diff --check
• ctest --test-dir cpp\build-gandiva-vs-conda-zlib -C Release -R gandiva-precompiled-test --output-on-failure

• GitHub Issue: [C++] Fix remaining overflow and negative length handling issues in Gandiva string functions #49973