[Rust][DataFusion] TO_TIMESTAMP function erroneously requires fractional seconds when no timezone is present

[asfimport]

Reported by @jhorstmann here: #8161 (comment)

One (not directly related) issue I noticed while trying this out, is that the local patterns seem to require the millisecond part, while for utc timestamps with "Z" they are optional:

Both of the following timestamps should be supported, but only the one with an explicit timestamp is:

> select to_timestamp('2020-09-12T10:30:00') from test limit 1;
ArrowError(ExternalError(General("Error parsing \'2020-09-12T10:30:00\' as timestamp")))

> select to_timestamp('2020-09-12T10:30:00Z') from test limit 1;
+-------------------------------------------+
| totimestamp(Utf8("2020-09-12T10:30:00Z")) |
+-------------------------------------------+
| 1599906600000000000                       |
+-------------------------------------------+

Reporter: Andrew Lamb / @alamb
Assignee: Andrew Lamb / @alamb

PRs and other links:

• GitHub Pull Request #8179

_{Note: This issue was originally created as ARROW-9986. Please see the migration documentation for further details.}

[asfimport]

Andy Grove / @andygrove:
Issue resolved by pull request 8179
#8179