[MERGE #3515 @MikeHolman] fix padding for rpc structs
[MERGE #3515 @MikeHolman] fix padding for rpc structs

Merge pull request #3515 from MikeHolman:idlcleanup

Implicit padding in structs causes RPC to go down slow path. I've gone through and fixed the padding in our structs so RPC will go down the happy path again.

mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore