Finish XCM Executor Assets w/ Tests (#1821)

* adding some basic tests

* min error

* fix min

* fix saturating_take

* all fungible and non fungible

* min abstract

* fix saturating take

* clean up

* some comments and fixes

* another fix

* more fixes

* comment

* remove unnecessary collect

* improve iter cloning

* better saturating_take impl

* feedback

* fix no_std build

* add doc tests

* mem::replace to be a bit more efficient

* better api

polkadot/xcm/xcm-executor/Cargo.toml

@@ -6,9 +6,8 @@ description = "An abstract and configurable XCM message executor."
 version = "0.8.22"
 
 [dependencies]
-codec = { package = "parity-scale-codec", version = "1.3.0", default-features = false, features = ["derive"] }
 impl-trait-for-tuples = "0.1.3"
-
+codec = { package = "parity-scale-codec", version = "1.3.0", default-features = false, features = ["derive"] }
 xcm = { path = "..", default-features = false }
 sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -21,10 +20,11 @@ frame-support = { git = "https://github.com/paritytech/substrate", branch = "mas
 default = ["std"]
 std = [
 	"codec/std",
-	"frame-support/std",
+	"xcm/std",
 	"sp-std/std",
 	"sp-io/std",
 	"sp-arithmetic/std",
 	"sp-core/std",
 	"sp-runtime/std",
+	"frame-support/std",
 ]