Introduce `LOG_TARGET` constants accross the code base

[bkchr]

Currently we have a mix between having LOG_TARGET constants declared in crates/files versus having certain crates/files where we declare the target every time manually. We should unify the code base to use LOG_TARGET everywhere. LOG_TARGET has the advantage of making it quite easy to search/filter for all log targets that Substrate supports.

Here an example where we have LOG_TARGET already defined:

substrate/primitives/trie/src/recorder.rs

Line 39 in 6e73c85

const LOG_TARGET: &str = "trie-recorder";

Here an example where we just write out the target:

substrate/primitives/state-machine/src/ext.rs

Line 218 in 6e73c85

target: "state",

[xlc]

This will help with #7067 as well. I can search const LOG_TARGET and know all the available targets

[bkchr]

Yes exactly.

[tonyalaribe]

I created a PR to use the const LOG_TARGET in more places. Could you take a look? #13116