coercion between decimal and other types lacking, compared to other numeric types

[kmitchener]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:
From test sql::expr::binary_mathematical_operator_with_null_lt

❯ select null + 1::decimal;
Plan("'Null + Decimal128(38, 10)' can't be evaluated because there isn't a common type to coerce the types to")

or (from the "test_string_concat_operator" test):

❯ select 'a' || 1.1::decimal;
Plan("'Utf8 || Decimal128(38, 10)' can't be evaluated because there isn't a common type to coerce the types to")

Expected behavior
A clear and concise description of what you expected to happen.

It should work like floats do:

❯ select null + 1::float;
+-----------------+
| NULL + Int64(1) |
+-----------------+
|                 |
+-----------------+
1 row in set. Query took 0.005 seconds.

❯ select 'a' || 1.1;
+---------------------------+
| Utf8("a") || Float64(1.1) |
+---------------------------+
| a1.1                      |
+---------------------------+
1 row in set. Query took 0.003 seconds.

Additional context
Add any other context about the problem here.

[liukun4515]

The NULL in the SQL syntax is associated with the DataType::NULL.
Now we don't support NULL data type with decimal data type yet.

But I think it is easy to support them.

I can help you to implement this.

@kmitchener

[liukun4515]

For select 'a' || 1.1::decimal; I think this should be support through the casting from decimal to utf8 #3478