Implemented FilterableValue for Option<FilterableValue>

[egormanga]

Description of Changes

• Resolves How to index an option field and filter by option value? #3992

API and ABI breaking changes

None.

Expected complexity level and risk

1.

Testing

• Manual testing
• Unit tests

[bfops]

Hey @egormanga, thank you for creating this.

Unfortunately, the full scope of FilterableValue is more expansive than it may first appear. See the augmented docs in https://github.com/clockworklabs/SpacetimeDB/pull/4024/files#diff-3ce7e5c02154d19ebe0624a457ea8b0c30a6b1658a24856ed1ea2ec3ee28916a.

[egormanga]

@bfops I assume this means that for Option<T> specifically we need to add special handling on the clients? JS will, for sure, treat and compare it as an object.