chore: Log warning for tests that are not really testing dictionary-encoded Parquet files

[andygrove]

Which issue does this PR close?

N/A

Rationale for this change

Many tests use the following pattern to cover testing with dictionary-encoded data.

    Seq("true", "false").foreach { dictionary =>
        withParquetTable(
          (-5 until 5).map(i => (i.toDouble + 0.3, i.toDouble + 0.8)),
          "tbl",
          withDictionary = dictionary.toBoolean) {

However, in many cases, including this example, the data does not contain repeated values and therefore does not cause any dictionary-encoded arrays to be created.

What changes are included in this PR?

Log a warning when withParquetTable is called with withDictionary=true and when the parquet file does not actually contain dictionary-encoded data.

I was originally going to add an assertion instead of a log message but it was too disruptive.

Example output from running tests:

- test multiple pages with mixed PLAIN_DICTIONARY and PLAIN encoding (prefetch enabled) (709 milliseconds)
- test multiple pages with mixed PLAIN_DICTIONARY and PLAIN encoding (524 milliseconds)
WARN: withParquetFile was called with withDictionary=true but did not write any dictionary-encoded columns
- skip vector re-loading (prefetch enabled) (669 milliseconds)
WARN: withParquetFile was called with withDictionary=true but did not write any dictionary-encoded columns

How are these changes tested?

No functional change to test. Manually tested that logging appears.

[parthchandra]

Did a lot of tests not have dictionary encoded data?
If the number is not large, might be better to fix the tests and throw an error here.

[comphead]

a nit: I feel this code checks if any column has RLE encoding, however RLE is on row group level? that means every page of the every column may or may not encoded. If lets say column C1 encoded, C2 nope, than no warning shown but we use exactly C2 for testing