[SPARK-13924][SQL] officially support multi-insert

## What changes were proposed in this pull request?

There is a feature of hive SQL called multi-insert. For example:
```
FROM src
INSERT OVERWRITE TABLE dest1
SELECT key + 1
INSERT OVERWRITE TABLE dest2
SELECT key WHERE key > 2
INSERT OVERWRITE TABLE dest3
SELECT col EXPLODE(arr) exp AS col
...
```

We partially support it currently, with some limitations: 1) WHERE can't reference columns produced by LATERAL VIEW. 2) It's not executed eagerly, i.e. `sql("...multi-insert clause...")` won't take place right away like other commands, e.g. CREATE TABLE.

This PR removes these limitations and make us fully support multi-insert.

## How was this patch tested?

new tests in `SQLQuerySuite`

Author: Wenchen Fan <wenchen@databricks.com>

Closes #11754 from cloud-fan/lateral-view.