bindings-macro: add custom index name to prevent index name collisions

[rudcode]

Description of Changes

SpacetimeDB generates colliding index names like product_category_id_idx_btree (category_id in product and id in product_category making same product_category_id prefix) , causing spacetime publish to fail with name used for multiple entities.

This PR allow users to specify custom index names:

// Before (error): index name collision
#[index(btree)]
pub category_id: u64,

// After (fix): specify unique name
#[index(btree, name = "product_category_id_idx_btree2")]
pub category_id: u64,

API and ABI breaking changes

None

Expected complexity level and risk

Complexity: 1
A simple change to only bindings-macro/src/table.rs. No breaking changes.

Testing

Manual testing with the reproducer from Issue #4719 - spacetime publish now succeeds when unique index names are provided. And when custom index name is changed, it successfully migrated.

[CLAassistant]

All committers have signed the CLA.

[rudcode]

I am just thinking, this maybe makes it hard to distinguish between old 1.x and 2.x syntax. Because old 1.x use name instead of accessor. This will remove all of the error when user wants to migrate from 1.x to 2.x. Do we need to rename the name to more explicit names like index_name?

[rudcode]

Force pushed to add error message if name is Ident (we assume it's old 1.x code that need migration). name should be LitStr