Add support for TRIM LEADING/TRAILING/BOTH syntax

[adsharma]

Which issue does this PR close?

Closes #935

Rationale for this change

What changes are included in this PR?

Implements the trim ( [ LEADING | TRAILING | BOTH ] [ FROM ] string text [, characters text ] ) syntax

Are there any user-facing changes?

Yes

[seddonm1]

hi @adsharma . this looks good and I think it is correct.

I am not sure your tests are proving anything additional? This would benefit from tests proving the trim ( [ LEADING | TRAILING | BOTH ] [ FROM ] string text [, characters text ] ) syntax. Maybe you could remove these tests and add some to tests/sql.rs which have ensure the SQL string -> function coverage like trim(both from 'yxTomxx', 'xyz').

[seddonm1]

looks good 👍

[alamb]

This looks great. Thank you for the contribution @adsharma and the review @seddonm1 👍

For anyone who is curious, it turns out that mysql and postgres differ in their treatment of TRIM but this PR follows the Postgres semantics which is the design goal for DataFusion. More details on #935 (comment)

[alamb]

Thanks again @adsharma -- this is a great first time contribution!