Various fixes for frame capture 1. Use contextId as identifier to separate captures for different GL context. 2. Fix write string params. In order to keep consistent between replay and capture, changes have been made to store C style string (with '\0' suffix) for string param capture, which breaks cpp frame capture. This change fixes it. 3. On Android device, it use a custom path to save captures and it breaks the loadBinaryData(). Here differentiate file name and file path to fix it. Bug: angleproject:3804 Change-Id: I378cf26697d15f0c1a8cf7afea2b758f5c58498b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1774469 Commit-Queue: Jiacheng Lu <lujc@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>