Unable to use projection alias in where filter

[sunng87]

What type of bug is this?

User Experience

What subsystems are affected?

Query Engine

Minimal reproduce step

For example, with this query

select json_get_string(greptime_value, "$.a") as b from vector_buffer_events where b > 's';

What did you expect to see?

It works.

What did you see instead?

We get error b is not a valid column for table vector_buffer_events

What operating system did you use?

any

What version of GreptimeDB did you use?

Relevant log output and stack trace