Add Mapping::take()

[SkymanOne]

This PR adds a new function Mapping::take() which retrieves and removed a value under the given key from the storage.

[HCastano]

Some small things, but generally looks good.

Also, do you know what the version of the contracts pallet introduced seal_take? We'll need to know so we can mention it in the release notes (oh btw, can you add an entry to the CHANGELOG for this)

[SkymanOne]

Some small things, but generally looks good.

Also, do you know what the version of the contracts pallet introduced seal_take? We'll need to know so we can mention it in the release notes (oh btw, can you add an entry to the CHANGELOG for this)

Yes.
https://github.com/paritytech/substrate/blob/master/frame/contracts/CHANGELOG.md#v300-2021-02-25

[codecov-commenter]

Codecov Report

Merging #1461 (6af6b9e) into master (60ba345) will increase coverage by 1.19%.
The diff coverage is 91.30%.

@@            Coverage Diff             @@
##           master    #1461      +/-   ##
==========================================
+ Coverage   45.77%   46.97%   +1.19%     
==========================================
  Files         201      201              
  Lines        6187     6210      +23     
==========================================
+ Hits         2832     2917      +85     
+ Misses       3355     3293      -62     

Impacted Files	Coverage Δ
crates/env/src/backend.rs	83.33% <ø> (ø)
crates/storage/src/lazy/mapping.rs	70.83% <66.66%> (-0.60%)	⬇️
crates/env/src/engine/off_chain/impls.rs	47.64% <87.50%> (+13.69%)	⬆️
crates/engine/src/ext.rs	67.97% <100.00%> (+9.98%)	⬆️
crates/env/src/api.rs	36.92% <100.00%> (+12.72%)	⬆️
crates/allocator/src/bump.rs	87.39% <0.00%> (+0.84%)	⬆️
crates/env/src/engine/off_chain/test_api.rs	64.70% <0.00%> (+5.88%)	⬆️
... and 3 more

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[HCastano]

Small nits with the wrapping, but otherwise looks good