[tree explain] Simplify display format of AggregateFunctionExpr #15252

Is your feature request related to a problem or challenge?

part of #14914

The output of AggregateExec also seems to contain redundant information.

┌─────────────┴─────────────┐
│       AggregateExec       │
│    --------------------   │
│   aggr: count(Int64(1))   │
│        mode: Final        │
└─────────────┬─────────────┘

Describe the solution you'd like

I debugged the code and found that the name of AggregateFunctionExpr is constructed in create_aggregate_expr_and_maybe_filter. In this function, debug information is generated for all Expr instances through Expr's SchemaDisplay.

To address this issue, I propose the following solution:

1. Add a new member sql_name to AggregateFunctionExpr.
2. Introduce a new method fmt_sql_name() for Expr, similar to schema_name(), and override it in AggregateFunction to generate sql_name.
3. Modify fmt_as in AggregateExec to output aggr_expr.sql_name instead of aggr_expr.name.

Describe alternatives you've considered

No response

Additional context

No response