  Add optional qualifier to Expr::Column

*Note*: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-10815

This follows on from https://issues.apache.org/jira/browse/ARROW-10732 and does the integration to complete the feature.

 

Expr::Column will be updated to

 
{code:java}
Column {
    /// Optional qualifier
    qualifier: Option<String>,
    /// Column name
    name: String,
}, {code}