Support type-coercion from Decimal to Float64

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

#[tokio::test]
async fn sql_abs_decimal() -> Result<()> {
    let ctx = SessionContext::new();
    register_decimal_csv_table_by_sql(&ctx).await;
    let sql = "SELECT abs(c1) from decimal_simple";
    let actual = execute_to_batches(&ctx, sql).await;

Fails with

Coercion from [Decimal(10, 6)] to the signature Uniform(1, [Float64, Float32]) failed.

Describe the solution you'd like
I would like the decimal to be coerced into a floating-point value.

Describe alternatives you've considered
None

Additional context
None

[comphead]

@andygrove Please check the PR

[comphead]

Opening new PR to resolve commit history