refactor: undo gas_limit renaming (#9558)

Chunk header `gas_limit` was renamed to `prev_gas_limit` in
#9500. After discussion with
@jakmeier I've realised while it is determined in the previous chunk, it
actually corresponds to gas limit for the current chunk.

chain/client/src/test_utils.rs

@@ -2351,7 +2351,7 @@ pub fn create_chunk(
             header.shard_id(),
             &mut rs,
             header.prev_gas_used(),
-            header.prev_gas_limit(),
+            header.gas_limit(),
             header.prev_balance_burnt(),
             tx_root,
             header.prev_validator_proposals().collect(),

core/primitives/src/sharding/shard_chunk_header_inner.rs

@@ -31,11 +31,11 @@ impl ShardChunkHeaderInner {
     }
 
     #[inline]
-    pub fn prev_gas_limit(&self) -> Gas {
+    pub fn gas_limit(&self) -> Gas {
         match self {
-            Self::V1(inner) => inner.prev_gas_limit,
-            Self::V2(inner) => inner.prev_gas_limit,
-            Self::V3(inner) => inner.prev_gas_limit,
+            Self::V1(inner) => inner.gas_limit,
+            Self::V2(inner) => inner.gas_limit,
+            Self::V3(inner) => inner.gas_limit,
         }
     }
 
@@ -144,8 +144,8 @@ pub struct ShardChunkHeaderInnerV1 {
     pub shard_id: ShardId,
     /// Gas used in the previous chunk.
     pub prev_gas_used: Gas,
-    /// Gas limit voted by validators in the previous chunk.
-    pub prev_gas_limit: Gas,
+    /// Gas limit voted by validators.
+    pub gas_limit: Gas,
     /// Total balance burnt in the previous chunk.
     pub prev_balance_burnt: Balance,
     /// Previous chunk's outgoing receipts merkle root.
@@ -171,8 +171,8 @@ pub struct ShardChunkHeaderInnerV2 {
     pub shard_id: ShardId,
     /// Gas used in the previous chunk.
     pub prev_gas_used: Gas,
-    /// Gas limit voted by validators in the previous chunk.
-    pub prev_gas_limit: Gas,
+    /// Gas limit voted by validators.
+    pub gas_limit: Gas,
     /// Total balance burnt in the previous chunk.
     pub prev_balance_burnt: Balance,
     /// Previous chunk's outgoing receipts merkle root.
@@ -198,8 +198,8 @@ pub struct ShardChunkHeaderInnerV3 {
     pub shard_id: ShardId,
     /// Gas used in the previous chunk.
     pub prev_gas_used: Gas,
-    /// Gas limit voted by validators in the previous chunk.
-    pub prev_gas_limit: Gas,
+    /// Gas limit voted by validators.
+    pub gas_limit: Gas,
     /// Total balance burnt in the previous chunk.
     pub prev_balance_burnt: Balance,
     /// Previous chunk's outgoing receipts merkle root.