chore(query): cast variant to other type allow cast JSON null as SQL NULL

[b41sh]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

cast variant to other type allow cast JSON null as SQL NULL

for example

root@0.0.0.0:48000/default> SELECT parse_json('123')::int64;
┌──────────────────────────┐
│ parse_json('123')::Int64 │
│      Nullable(Int64)     │
├──────────────────────────┤
│                      123 │
└──────────────────────────┘
1 row read in 0.019 sec. Processed 1 row, 1 B (52.63 rows/s, 52 B/s)

root@0.0.0.0:48000/default> SELECT parse_json('null')::int64;
┌───────────────────────────┐
│ parse_json('null')::Int64 │
│      Nullable(Int64)      │
├───────────────────────────┤
│                      NULL │
└───────────────────────────┘
1 row read in 0.019 sec. Processed 1 row, 1 B (52.63 rows/s, 52 B/s)

• fixes: Issue while casting to BIGINT #17388

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

---

This change is