Use proc macros to generate conversion functions for MultiLocation (#3635)

* Use proc macros to generate conversion functions for MultiLocation

* Add compile test and missing conversion cases

* Add common derives for Parent and Ancestor

* Generate conversion functions for MultiLocation v0 via proc macro

* Add type conversion test and fix a bug

* cargo fmt

* Do not hardcode 8 as the number of max parents

* Use map instead of for loops when generating code fragments

* Spelling

* cargo fmt

* More mapping, less for-looping

polkadot/Cargo.lock

@@ -11775,6 +11775,7 @@ dependencies = [
  "impl-trait-for-tuples",
  "log",
  "parity-scale-codec",
+ "xcm-procedural",
 ]
 
 [[package]]
@@ -11835,6 +11836,15 @@ dependencies = [
  "xcm-executor",
 ]
 
+[[package]]
+name = "xcm-procedural"
+version = "0.1.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "xcm-simulator"
 version = "0.9.9"