Code generate filter function for non-unique indexes

[aasoni]

Description of Changes

Update typescript code generation to generate accessors on non unique indexes. These will use the filter function as is the convention in C# and module api.

Related to #1387 but doesn't close it.

API and ABI breaking changes

Expected complexity level and risk

2

Testing

Generated the following table:

#[spacetimedb::table(
    name = test_index,
    index(name = multi_column_test, btree(columns = [identity, col_1, col_2, col_3, col_4])), 
    public,
)]
#[derive(Clone)]
pub struct TestIndex {
    #[primary_key]
    #[auto_inc]
    pub id: u64,

    pub identity: Identity,
    pub col_1: u64,
    pub col_2: i32,
    pub col_3: f32,
    pub col_4: String,
}

Into typescript which resulted in the following code for index lookups:

  /**
   * Access to the `id` index on the table `test_index`,
   * with `ctx.db.testIndex.id.find(...)`.
   */
  id = {
    // Find the subscribed row matching the lookup value if present in the client cache.
    find: (col_vals: bigint): TestIndex | undefined => {
      for (let row of this.tableCache.iter()) {
        if (__deepEqual(row.id, col_vals)) {
          return row;
        }
      }
    },
  };
  /**
   * Access to the `multiColumnTest` index on the table `test_index`,
   * with `ctx.db.testIndex.multiColumnTest.filter(...)`.
   */
  multiColumnTest = {
    // Find the subscribed row matching the lookup value if present in the client cache.
    filter: (col_vals: [__Identity,bigint,number,number,string]): TestIndex[] => {
      const result: TestIndex[] = [];
      for (let row of this.tableCache.iter()) {
        if (__deepEqual([row.identity,row.col1,row.col2,row.col3,row.col4], col_vals)) {
          result.push(row);
        }
      }
      return result;
    },
  };

I then manually inserted values into the test_index table and checked that calling the new filter and find functions returned the expected values.