Shader: Add missing switch cases to operationString
Shader: Add missing switch cases to operationString

These used to assert.
Instead of asserting, let the compiler warn about unhandled cases - there's already a `return "<unknown>"` statement below the switch.

Credit to Dan Sinclair who did all the hard work here.

Bug: None - maintenance fix for legacy code
Change-Id: I010a1d6228961a80a15523ff1a2c6db522b7756d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40833
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>
Tested-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>

google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader