feat: replace Schema with FieldLayout for contract internals (#1336)

Co-authored-by: Kevin Ingersoll <kingersoll@gmail.com>
Co-authored-by: alvrs <alvarius@lattice.xyz>

.changeset/grumpy-files-heal.md

@@ -0,0 +1,28 @@
+---
+"@latticexyz/cli": major
+"@latticexyz/protocol-parser": minor
+"@latticexyz/store": major
+"@latticexyz/world": major
+---
+
+- Add `FieldLayout`, which is a `bytes32` user-type similar to `Schema`.
+
+  Both `FieldLayout` and `Schema` have the same kind of data in the first 4 bytes.
+
+  - 2 bytes for total length of all static fields
+  - 1 byte for number of static size fields
+  - 1 byte for number of dynamic size fields
+
+  But whereas `Schema` has `SchemaType` enum in each of the other 28 bytes, `FieldLayout` has static byte lengths in each of the other 28 bytes.
+
+- Replace `Schema valueSchema` with `FieldLayout fieldLayout` in Store and World contracts.
+
+  `FieldLayout` is more gas-efficient because it already has lengths, and `Schema` has types which need to be converted to lengths.
+
+- Add `getFieldLayout` to `IStore` interface.
+
+  There is no `FieldLayout` for keys, only for values, because key byte lengths aren't usually relevant on-chain. You can still use `getKeySchema` if you need key types.
+
+- Add `fieldLayoutToHex` utility to `protocol-parser` package.
+
+- Add `constants.sol` for constants shared between `FieldLayout`, `Schema` and `PackedCounter`.