Allowing omitting the "T" separator from a datetime string

[riverszhang89]

Our customers have issue using spark to create a dataframe on a datetime column, because spark interpolates the provided datetime string, but drops the "T" separator when filling the range.

It seems that omitting the "T" character is fairly acceptable, and ISO 8601 does allow it to be omitted in a few cases. This is a very simple patch to allow it.

[roborivers]

Coding style check: Error. ⚠.
Smoke testing: Success ✓.
Cbuild submission: Error ⚠.
Regression testing: 3/625 tests failed ⚠.

The first 10 failing tests are:
udf
consumer_non_atomic_default_consumer_generated
consumer

[dorinhogea]

If we allow strings without T to be converted to datetimes, we have the following conundrum: is "20250101" a datetime or an epoch value?

[riverszhang89]

If we allow strings without T to be converted to datetimes, we have the following conundrum: is "20250101" a datetime or an epoch value?

If the string contains only digits, it's treated as a unix timestamp (code). So "20250101" will still be an epoch value! I've also added a test for it!

[roborivers]

Coding style check: Error. ⚠.
Smoke testing: Success ✓.
Cbuild submission: Success ✓.
Regression testing: 5/625 tests failed ⚠.

The first 10 failing tests are:
sc_transactional_rowlocks_generated
udf
consumer_non_atomic_default_consumer_generated
consumer
sc_downgrade

[akshatsikarwar]

This breaks UDF and consumer tests?

[riverszhang89]

This breaks UDF and consumer tests?

There's one case that I overlooked, eg 2025-01-01 UTC. Apparently the type code expects that a timezone has a leading space. But because we now additionally allow spaces in between the date portion and the rest of the datetime, we may not have a leading space when we read the timezone. for instance:

2025-01-01 UTC
          ^ old code would stop here, timezone would be "[space]UTC"
   vs
   
2025-01-01 UTC
           ^ new code stops here, timezone is "UTC"

[roborivers]

Coding style check: Error. ⚠.
Smoke testing: Success ✓.
Cbuild submission: Success ✓.
Regression testing: 2/625 tests failed ⚠.

The first 10 failing tests are:
cdb2_close
sc_downgrade