Move assert_batches_eq! macros to test_utils.rs

[alamb]

Which issue does this PR close?

Closes #745, re #743

Rationale for this change

The assert_batches_eq! and assert_batches_sorted_eq! macros are used to write easier to maintain tests. However, the macros are in the test module that is only compiled for tests of the datafusion crate and are not, therefore, available to the "integration" style tests in sql.rs

#[cfg(test)]
pub mod test;

I also find them so useful they are also in IOx in test_utils.rs

BTW the reason they are "easier to maintain tests" is that you can copy the output directly from the test failure into the code to update the results (rather than having to reformat it manually). For example, to generate the new output in sql.rs, I simply put a placeholder in and ran the test and then copy/pasted in the output of the test:

---- parquet_query stdout ----
thread 'parquet_query' panicked at 'assertion failed: `(left == right)`
  left: `["foo"]`,
 right: `["+----+--------------------------+", "| id | CAST(string_col AS Utf8) |", "+----+--------------------------+", "| 4  | 0                        |", "| 5  | 1                        |", "| 6  | 0                        |", "| 7  | 1                        |", "| 2  | 0                        |", "| 3  | 1                        |", "| 0  | 0                        |", "| 1  | 1                        |", "+----+--------------------------+"]`: 

expected:

[
    "foo",
]
actual:

[
    "+----+--------------------------+",
    "| id | CAST(string_col AS Utf8) |",
    "+----+--------------------------+",
    "| 4  | 0                        |",
    "| 5  | 1                        |",
    "| 6  | 0                        |",
    "| 7  | 1                        |",
    "| 2  | 0                        |",
    "| 3  | 1                        |",
    "| 0  | 0                        |",
    "| 1  | 1                        |",
    "+----+--------------------------+",
]

', datafusion/tests/sql.rs:121:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

What changes are included in this PR?

1. Move the he assert_batches_eq! and assert_batches_sorted_eq! macros to test_utils.rs
2. port one test in sql.rs to demonstrate their use

Are there any user-facing changes?

The assert_batches_eq! and assert_batches_sorted_eq! macros are now part of the DataFusion public API

Follow on work is tracked in #743