Reexport scale dependencies, introduce #[ink::scale_derive]

[ascjones]

Closes #1885.

Removes requirement for contracts to have direct dependencies on parity-scale-codec and scale-info, instead using reexports from the ink umbrella crate. This require some additional attributes e.g. #[codec(crate = ::ink::scale)] to specify the path of the reexported crate for the built in derives.

To this end I have added a convenience attribute macro to add the necessary attributes:instead of doing derive(Encode, Decode) or derive(TypeInfo), simply:

#[ink::scale_derive(Encode, Decode, TypeInfo)]

This would expand to

#[derive(::ink::scale::Encode, ::ink::scale::Decode)]
#[codec(crate = ::ink::scale)]
#[cfg_attr(
  feature = "std", 
  derive(::scale_info::TypeInfo),
  scale_info(crate = ::ink::scale_info)
)]

todo

• update all examples, remove scale dependencies
• document use of ink::scale_derive
• ui tests for scale_derive macro

[SkymanOne]

#[ink::scale_derive(encode, decode, type_info)]

Can we make derive specs to be camel case?

[ascjones]

#[ink::scale_derive(encode, decode, type_info)]

Can we make derive specs to be camel case?

We could. I had to decide between idiomatic attribute configuration snake_case and aping the special case derive which uses the CamelCase trait names.

I was in two minds and decided to go with the idiomatic attribute config style, on the basis that it is clear what is happening and no magic. Could possibly be persuaded to do use CamelCase based on it being closer to the derive syntax, itself: question is whether that is a good or a bad thing.

[codecov-commenter]

Codecov Report

Merging #1890 (a395df9) into master (ff4a0b5) will decrease coverage by 0.06%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1890      +/-   ##
==========================================
- Coverage   52.96%   52.90%   -0.06%     
==========================================
  Files         215      220       +5     
  Lines        6786     6822      +36     
==========================================
+ Hits         3594     3609      +15     
- Misses       3192     3213      +21     

Files Changed	Coverage Δ
crates/env/src/call/create_builder.rs	2.66% <ø> (ø)
...odegen/src/generator/as_dependency/call_builder.rs	0.00% <ø> (ø)
...odegen/src/generator/as_dependency/contract_ref.rs	0.00% <ø> (ø)
...rates/ink/codegen/src/generator/chain_extension.rs	0.00% <ø> (ø)
crates/ink/codegen/src/generator/dispatch.rs	0.00% <ø> (ø)
crates/ink/codegen/src/generator/event.rs	0.00% <ø> (ø)
crates/ink/codegen/src/generator/storage_item.rs	0.00% <ø> (ø)
...nk/codegen/src/generator/trait_def/call_builder.rs	0.00% <ø> (ø)
.../codegen/src/generator/trait_def/call_forwarder.rs	0.00% <ø> (ø)
crates/ink/macro/src/lib.rs	0.00% <0.00%> (ø)
... and 22 more

... and 5 files with indirect coverage changes

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[ascjones]

#[ink::scale_derive(encode, decode, type_info)]

Can we make derive specs to be camel case?

Done.