[SPARK-16374][SQL] Remove Alias from MetastoreRelation and SimpleCatalogRelation

#### What changes were proposed in this pull request?
Different from the other leaf nodes, `MetastoreRelation` and `SimpleCatalogRelation` have a pre-defined `alias`, which is used to change the qualifier of the node. However, based on the existing alias handling, alias should be put in `SubqueryAlias`.

This PR is to separate alias handling from `MetastoreRelation` and `SimpleCatalogRelation` to make it consistent with the other nodes. It simplifies the signature and conversion to a `BaseRelation`.

For example, below is an example query for `MetastoreRelation`,  which is converted to a `LogicalRelation`:
```SQL
SELECT tmp.a + 1 FROM test_parquet_ctas tmp WHERE tmp.a > 2
```

Before changes, the analyzed plan is
```
== Analyzed Logical Plan ==
(a + 1): int
Project [(a#951 + 1) AS (a + 1)#952]
+- Filter (a#951 > 2)
   +- SubqueryAlias tmp
      +- Relation[a#951] parquet
```
After changes, the analyzed plan becomes
```
== Analyzed Logical Plan ==
(a + 1): int
Project [(a#951 + 1) AS (a + 1)#952]
+- Filter (a#951 > 2)
   +- SubqueryAlias tmp
      +- SubqueryAlias test_parquet_ctas
         +- Relation[a#951] parquet
```

**Note: the optimized plans are the same.**

For `SimpleCatalogRelation`, the existing code always generates two Subqueries. Thus, no change is needed.

#### How was this patch tested?
Added test cases.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14053 from gatorsmile/removeAliasFromMetastoreRelation.