Add support for events and indexed fields.

This adds two new attributes: `#[event]` and `#[indexed]`.

The `#[event]` attribute marks a struct or enum as an event that can be
emitted by a contract.

The `#[indexed]` attribute can be applied to fields within structs that
are attributed with `#[event]`. This is particularly useful for event
structs, allowing for efficient filtering and searching of emitted
events based on the values of these fields.

When using this attribute, the indexed fields must be applied
sequentially to the initial set of fields in a struct.

This attribute can only be applied to fields whose type is an exact size
ABI type. The exact size ABI types include:

- `bool`
- `u8`, `u16`, `u32`, `u64`, `u256`
- `numeric`
- `b256`
- `str[N]`
- Tuples containing only exact size types
- Structs containing only exact size types
- Arrays of exact size types with a literal length
- Type aliases to exact size types

Additionally it causes the event types to be included in the JSON ABI
representation for the contract.

```sway
struct MyEventStruct {
    #[indexed]
    id: u64,
    sender: Identity,
}

enum MyEventEnum {
    A: (),
    B: (),
}
```

Additionally this updates the JSON ABI to emit an `offset` for indexed
fields.

Author: tritao

.github/workflows/scripts/check-dep-versions/src/main.rs

@@ -9,7 +9,7 @@ const REQUIRED_XYZ_DEP: &str = "fuel-core-client";
 
 // Dependency names allowed (but not required) to use x.y.z format
 // Add names of common dev-dependencies here if you want to allow x.y.z for them
-const ALLOWED_XYZ_DEPS: &[&str] = &["etk-asm", "etk-ops", "dap"];
+const ALLOWED_XYZ_DEPS: &[&str] = &["etk-asm", "etk-ops", "dap", "fuel-abi-types"];
 
 // Regex to strictly match semantic version x.y.z (no prefixes like ^, ~)
 const XYZ_REGEX_STR: &str = r"^\d+\.\d+\.\d+([\w.-]*)$"; // Allow suffixes like -alpha, .1