Adds new execution strategy nativeElseWasm (#1546)

* fix: adds new execution strategy nativeElseWasm and replace nativeWhenPossible with it

* feat: adds cmd line params for execution strategies

* fix: uses of cmd line execution strategies

* chore: remove white spaces

* chore: remove println

* chore: remove whitespace

* fix: generating functions with context

* feat: add function to generate with_context declarations

* fix: add implementation for with_context function calls

* fix: add execution context to call_api_at function

* fix: making use of context to select strategy for block_builder

* chore: cleaning up

* fix: merging issues

* fix tests

* add wasm files

* chore: small doc for context fields

* chore: delete redundant docs

* fix: use full path for ExecutionContext

* fix: add context functions from inside fold_item_impl

* chore: remove clone

* fix: moving generative function to utils, remove unused imports

* fix: add missing full path for ExecutionContext

* fix: merge issues

* update wasm files

* fix: update to keep up with changes in master

* chore: remove unused functions, clean up

* fix test

* fix grumbles

* fix: add more tests

* fix: some refactorings

* feat: add execution strategy to call

* chore: small improvements

* fix: add message to panic

* fix tests

substrate/core/client/src/genesis.rs

@@ -93,7 +93,7 @@ mod tests {
 			&executor(),
 			"Core_initialise_block",
 			&header.encode(),
-			ExecutionStrategy::NativeWhenPossible,
+			ExecutionStrategy::NativeElseWasm,
 		).unwrap();
 
 		for tx in transactions.iter() {
@@ -104,7 +104,7 @@ mod tests {
 				&executor(),
 				"BlockBuilder_apply_extrinsic",
 				&tx.encode(),
-				ExecutionStrategy::NativeWhenPossible,
+				ExecutionStrategy::NativeElseWasm,
 			).unwrap();
 		}
 
@@ -115,7 +115,7 @@ mod tests {
 			&executor(),
 			"BlockBuilder_finalise_block",
 			&[],
-			ExecutionStrategy::NativeWhenPossible,
+			ExecutionStrategy::NativeElseWasm,
 		).unwrap();
 		header = Header::decode(&mut &ret_data[..]).unwrap();
 		println!("root after: {:?}", header.extrinsics_root);
@@ -159,7 +159,7 @@ mod tests {
 			&executor(),
 			"Core_execute_block",
 			&b1data,
-			ExecutionStrategy::NativeWhenPossible,
+			ExecutionStrategy::NativeElseWasm,
 		).unwrap();
 	}
 
@@ -210,7 +210,7 @@ mod tests {
 			&Executor::new(None),
 			"Core_execute_block",
 			&b1data,
-			ExecutionStrategy::NativeWhenPossible,
+			ExecutionStrategy::NativeElseWasm,
 		).unwrap();
 	}
 }