Name event parameters

[xlc]

Currently event parameters are unnamed, so the only way to know the meaning of each value is by looking at the type and docs.

It will be good if there is a way annotate the parameter name in metadata so SDK can generate named accessor.

For now we are going to try to parse the doc comments to look something like (from, to, value) to get the name, but it does not always work.

substrate/frame/balances/src/lib.rs

Line 226 in 7217ab6

/// Transfer succeeded (from, to, value).

[bkchr]

This can come with #5678