`trunc(decimal)` produces unexpected/wrong results above 2^53

[neilconway]

Describe the bug

There is actually no implementation of trunc for decimal inputs, so we coerce the input to floating point. This yields incorrect/unexpected results for inputs above 2^53.

To Reproduce

> select trunc(CAST(9007199254740993 AS DECIMAL(20,0)));
+--------------------------------+
| trunc(Int64(9007199254740993)) |
+--------------------------------+
| 9007199254740992.0             |
+--------------------------------+
1 row(s) fetched.
Elapsed 0.011 seconds.

Expected behavior

The query should return 9007199254740993, which is what Postgres and DuckDB both do.

Additional context

No response

[neilconway]

take