Disable EnsureLoopForwardProgressTest on iOS The CL[1] that enabled the optimization of simple loops introduced the EnsureLoopForwardProgressTest. However, this test relies on SH_ESSL_OUTPUT, which requires angle_enable_essl to be enabled. Since this is not currently supported on iOS, this CL disables the test on iOS until a proper solution is found. [1] https://chromium-review.googlesource.com/c/angle/angle/+/6575051 Bug: b/426055001 Change-Id: If694be82bad4b4724ace5051c9ee38829a367170 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6703073 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>