The percentile argument for ApproxPercentileCont must be Float64, not Decimal128(2, 1)

[andygrove]

Describe the bug
I found this when testing #4102. csv_query_approx_percentile_cont fails with:

The percentile argument for ApproxPercentileCont must be Float64, not Decimal128(2, 1)

To Reproduce
Run tests in #4102

Expected behavior
I assume we need to add type coercion to convert function args to the correct type

Additional context

[comphead]

@andygrove please assign this to me

[comphead]

Local test to reproduce

#[tokio::test]
async fn test_approx_percentile_cont() -> Result<()> {
    let ctx = SessionContext::new();
    register_aggregate_csv(&ctx).await?;
    let sql = "SELECT approx_percentile_cont(c2, cast(1.0 as decimal(10,2))) FROM aggregate_test_100";
    execute_to_batches(&ctx, sql).await;

    Ok(())
}