[gRPC] Design support for controlling integral type encodings #631

Protobuf supports many integer types, and most types control the encoding of the integer as part of the binary-packed protobuf message.

• int32 / int64 : variable-length 32/64 bit signed integers, inefficient for negative numbers
• uint32 / uint64 : variable-length 32/64 bit unsigned integers
• sint32 / sint64 variable-length 32/64 bit signed integers, more efficient for negative numbers
• fixed32/fixed64 fixed-length 4/8 byte unsigned integer, more efficient than uint32/uint64 if values are often greater than 2^{28} / 2^{56}
• sfixed32/sfixed64 fixed-length 32/64 bit signed integers, always 4/8 bytes

In the prototype, we are mapping Cadl int32/int64/uint32/uint64 to the same-named types in Protobuf, but we should expose these encoding knobs to developers, since they can have a big impact on the performance characteristics of a service.