Unique trait id as a parameter for CallBuilder trait impls

[ascjones]

Yet another solution for #982, as an alternative to #983 and #1136.

It is similar to #1136 except that it uses a unique id generated for the trait an by XOR of the trait selectors, which should be unique. As suggested by @xgreenx.

[paritytech-cicd-pr]

🦑 📈 ink! Example Contracts ‒ Changes Report 📉 🦑

These are the results when building the examples/* contracts from this branch with cargo-contract 0.17.0-438b31d and comparing them to ink! master:

	Δ Optimized Size	Δ Used Gas	Total Optimized Size	Total Used Gas
accumulator			1.35 K
adder			2.47 K
contract-terminate			1.23 K	215_704
contract-transfer			8.47 K	15_704
delegator			6.86 K	50_833
dns			9.70 K	47_112
erc1155			28.12 K	94_224
erc20			9.34 K	47_112
erc721			13.17 K	125_632
flipper			1.63 K	15_704
incrementer			1.56 K	15_704
multisig			26.25 K	102_922
proxy			3.36 K	32_147
rand-extension			4.64 K	15_704
subber			2.48 K
trait-erc20			9.64 K	47_112
trait-flipper			1.41 K	15_704
trait-incrementer			1.54 K	31_408

Link to the run | Last update: Fri Feb 18 18:43:11 CET 2022

[xgreenx]

I'm okay with all three changes=) But between second and third I prefer third=)

[HCastano]

Yeah, this is my preferred solution as well!