implement actor::is_builtin_actor(Cid) -> int32 syscall

[raulk]

Some built-in actors reference the CodeCID of other actors. Concretely:

• the init actor holds an allowlist of actors it is allowed to construct (multisig, paych)
• the market and miner actors validate that only "signable" actors (account, multisig) can perform certain duties
• the market actor validate that only the miner actor can perform deal management operations
• the power actor validates that only the miner actor can perform privileged operations

Prior to FVM, CodeCIDs were hardcoded, but with the introduction of Wasm bytecode as a portable execution format, CodeCIDs for the first time will truly content-address executable payloads. Unfortunately, this means that actors will need to learn the CodeCIDs of other actor in a more dynamic way.

We considered various solutions like:

• Architecting the build process in https://github.com/filecoin-project/builtin-actors in layers and injecting CodeCIDs values as deterministically-named env variables that could be read at compile time. However, cyclic dependencies make this impossible.
• Introducing a fully-fledged actor registry: Name System Design Discussion FIPs#297
• Injecting known actor CodeCIDs as imported globals in Wasm bytecode.

Ultimately we settled on introducing a new infallible syscall:

actor::is_builtin_actor(Cid) -> i32

Where the input is a CodeCID, and the return value represents the matched builtin actor type:

i32	Actor type
0	Unknown
1	System
2	Init
3	Cron
4	Account
5	Power
6	Miner
7	Market
8	Payment channel
9	Multisig
10	Reward
11	Verified registry