[feature] #2488: Add support for trait impls in ffi_export

[Erigara]

Description of the Change

• Add support for trait impls (methods are generated with following name Type__Trait__method)
• Remove requirements for items to have doc string

Issue

Closes #2488.

Benefits

No need to manually implement trait methods.

Possible Drawbacks

None.

Usage Examples or Tests [optional]

cargo +nightly-2022-04-20 miri test --package iroha_ffi

Alternate Designs [optional]

[codecov]

Codecov Report

Merging #2601 (e5e9c99) into iroha2-dev (a16d9c3) will decrease coverage by 1.72%.
The diff coverage is 63.31%.

❗ Current head e5e9c99 differs from pull request most recent head 250134c. Consider uploading reports for the commit 250134c to get more accurate results

@@              Coverage Diff               @@
##           iroha2-dev    #2601      +/-   ##
==============================================
- Coverage       67.61%   65.88%   -1.73%     
==============================================
  Files             140      156      +16     
  Lines           26173    28155    +1982     
==============================================
+ Hits            17696    18550     +854     
- Misses           8477     9605    +1128     

Impacted Files	Coverage Δ
cli/derive/src/lib.rs	74.72% <ø> (ø)
cli/src/torii/mod.rs	28.88% <ø> (ø)
cli/src/torii/routing.rs	69.92% <0.00%> (-2.87%)	⬇️
client/src/client.rs	43.36% <0.00%> (-2.96%)	⬇️
client_cli/src/main.rs	0.26% <ø> (ø)
config/base/src/runtime_upgrades.rs	35.63% <ø> (ø)
core/src/block.rs	70.00% <ø> (ø)
core/src/queue.rs	95.67% <ø> (-0.08%)	⬇️
core/src/smartcontracts/isi/asset.rs	54.82% <ø> (ø)
core/src/smartcontracts/wasm.rs	95.39% <ø> (+0.12%)	⬆️
... and 154 more

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[appetrosyan]

Suggested change

	"Methods defined in the inherit impl block must be public"
	"Methods defined in the inherent `impl` block must be public"

On another note, I'd actually prefer if you just skipped them, instead of failing to compile. Notify via https://docs.rs/proc-macro-error/latest/proc_macro_error/macro.emit_warning.html

[Erigara]

We are aborting execution all over the place (i mean ffi_export/import macros) where we don't support such item.
What benefits will we get if we skip private functions?

[appetrosyan]

Basically, you wouldn't force the user to add the function elsewhere. A private function is perfectly valid code, while it shouldn't be reflected in the ffi export, forcing people to have multiple inherent impls is not good design.

[Erigara]

Ok, in this case we should make impl blocks more permissive in general, skip consts, types, ... instead of aborting execution.

[appetrosyan]

exactly.

[Erigara]

Now private functions are skipped, however i left this abortion, to indicate that something going wrong if we try to export private function.