[SPARK-16448] RemoveAliasOnlyProject should not remove alias with metadata

## What changes were proposed in this pull request?

`Alias` with metadata is not a no-op and we should not strip it in `RemoveAliasOnlyProject` rule.
This PR also did some improvement for this rule:

1. extend the semantic of `alias-only`. Now we allow the project list to be partially aliased.
2. add unit test for this rule.

## How was this patch tested?

new `RemoveAliasOnlyProjectSuite`

Author: Wenchen Fan <wenchen@databricks.com>

Closes #14106 from cloud-fan/bug.