fix: Protect column and row validation calculated column names from Oracle 30 character identifier limit

[nj1973]

This protects all engines not just Oracle 12.1 and below. It's just that Oracle 12.1 and below have a 30 character limit which we almost always cross for row validation. Other engines have a 128 character identifier limit and therefore are less likely to be breached.

This PR introduces the following change:

1. Identify the maximum identifier length for both source and target engines and take the lowest one as the ceiling for the validation.
2. When prefixing a column alias with an operation, such as sum__, ifnull__ etc, we compare the length of the resulting name with the maximum length.
3. If the new name breaches the maximum then a simplified alias is used. The simplified alias uses the column position in place of its name.
4. This has been done for both concat/hash row validation and aggregate column validation.
5. I've added unit tests for the name shortening logic.
6. Ideally we could do with adding integration tests for Oracle 11g, I think this can happen outside of this issue.

Example of column validation SQL from new logic:

SELECT count(:count_1) AS count
, max(t0.id) AS max__id
, max(t0.col_dec_long_123456789012345) AS max__dvt_calc_col_1
, max(t0.length__dvt_calc_col_4) AS max__length__dvt_calc_col_4
FROM (
  SELECT t1.id AS id
  , t1.col_dec_long_123456789012345 AS col_dec_long_123456789012345
  , t1.col_dec2_long_123456789012345 AS col_dec2_long_123456789012345
  , t1.col_date_long_1234567890 AS col_date_long_1234567890
  , t1.col_string_long_1234567890 AS col_string_long_1234567890
  , length(t1.col_string_long_1234567890) AS length__dvt_calc_col_4
  FROM dvt_test.tab_long_cols t1
) t0

Note that:

• length__dvt_calc_col_4 is introduced at depth 1 because the length of length__col_string_long_1234567890 would cross 30 characters
• The max__ alias is then applied to the length column at depth 0: max__length__dvt_calc_col_4
• The max__ alias is applied to the decimal column at depth 0 because the length of max__col_dec_long_123456789012345 would cross 30 characters
• max__id is unaffected because it remains below 30 characters

The same logic would be seen in a row validation too but more functions are applied so we're more likely to see dvt_calc_col columns. It's worth pointing out that this is only visible in the SQL statement, the end report still uses proper column names.

[nj1973]

/gcbrun

[nj1973]

/gcbrun

[nehanene15]

LGTM!