[SPARK-22543][SQL] fix java 64kb compile error for deeply nested expressions

## What changes were proposed in this pull request?

A frequently reported issue of Spark is the Java 64kb compile error. This is because Spark generates a very big method and it's usually caused by 3 reasons:

1. a deep expression tree, e.g. a very complex filter condition
2. many individual expressions, e.g. expressions can have many children, operators can have many expressions.
3. a deep query plan tree (with whole stage codegen)

This PR focuses on 1. There are already several patches(#15620  #18972 #18641) trying to fix this issue and some of them are already merged. However this is an endless job as every non-leaf expression has this issue.

This PR proposes to fix this issue in `Expression.genCode`, to make sure the code for a single expression won't grow too big.

According to maropu 's benchmark, no regression is found with TPCDS (thanks maropu !): https://docs.google.com/spreadsheets/d/1K3_7lX05-ZgxDXi9X_GleNnDjcnJIfoSlSCDZcL4gdg/edit?usp=sharing

## How was this patch tested?

existing test

Author: Wenchen Fan <wenchen@databricks.com>
Author: Wenchen Fan <cloud0fan@gmail.com>

Closes #19767 from cloud-fan/codegen.