read runtime version from code wasm custom sections

[qdm12]

For newer runtimes, the runtime version can now be obtained from the WASM custom sections from the wasm code, and there is no longer a need to instantiate the full runtime to check its version.

For context:

• Incorporate feedback from Parity w3f/polkadot-spec#524
• Embed version (or other metadata) into runtime wasm blob paritytech/substrate#7327
• Embed runtime version as a custom section paritytech/substrate#8688

Note reading the runtime version by instantiating it and calling Core_version still need to be supported for older runtimes.

So the process should be:

1. try to find versions from the wasm custom section
2. fallback to instantiating + calling Core_version on the instance

[timwu20]

This is an optimization that isn't required for any milestone at the moment.