Features needed for reserve-backed stablecoins (#7152)

* Features needed for reserve-backed stablecoins

* Builds & tests.

* Double map for an efficient destroy.

* Update frame/assets/src/lib.rs

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

* ED/zombie-count/refs

Feature: ED/minimum balance enforcement
Feature: enforce zombie count
Feature: allow system-alive accounts to exist, but add reference

* Update frame/assets/src/lib.rs

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

* Update frame/assets/Cargo.toml

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* Docs

* Some tests

* More tests

* Allow for max_zombies to be adjusted

* Test for set_max_zombies

* Tests and a couple of fixes

* First few benchmarks

* Benchmarks.

* Fix error message in test

* Fixes

* Fixes

* Fixes

* cargo run --release --features runtime-benchmarks --manifest-path bin/node/cli/Cargo.toml -- benchmark --chain dev --steps 50 --repeat 20 --extrinsic * --execution=wasm --wasm-execution=compiled --output ./bin/node/runtime/src/weights --header ./HEADER --pallet pallet_assets

* Update frame/assets/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fixes

* Fixes

* Fixes

* cargo run --release --features runtime-benchmarks --manifest-path bin/node/cli/Cargo.toml -- benchmark --chain dev --steps 50 --repeat 20 --extrinsic * --execution=wasm --wasm-execution=compiled --output ./bin/node/runtime/src/weights --header ./HEADER --pallet pallet_assets

* Fixes

* Update default weight

* Add proper verification to benchmarks

* minor improvements to tests

* Update frame/assets/src/benchmarking.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Fix

* New weights system

* fix compile

* cargo run --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_assets --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/assets/src/weights.rs --template=./.maintain/frame-weight-template.hbs

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>
Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>
Co-authored-by: Parity Benchmarking Bot <admin@parity.io>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>