RcpSqrt_pp is not accurate enough to be used on non-relaxed precision types.

Bug: b/126873455
Tests: dEQP-VK.glsl.builtin.precision.inversesqrt.*
Change-Id: I3e34d28dbd863c9cb14cf6c79afe08a1992b5478
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28697Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>