Support ranking window functions

[dai-chen]

Issue #, if available: #751

Description of changes: This PR is to add basic support for ranking window functions.

1. Add window operator and related code changes: AST/logical/physical window operator, visitor and other util code.
2. Add ranking window functions: ROW_NUMBER, RANK and DENSE_RANK.
3. Rename PPL_ASC/DESC to DEFAULT_ASC/DESC.

To-Dos: Window function name: for now toString() is used as symbol name. This restricts multiple use of same window function, ex. SELECT RANK() OVER(...), RANK() OVER(...).

Design: In Abstract Syntax Tree (AST), the window function is still on the project item list in Project AST node. After analyzing, it is separated into an individual logical Window operator with window function and its definition along with Sort operator that guarantee order of input data of window operator. Eventually both converts to its correspondent physical operators.

Testing: Add UT and comparison test: https://github.com/dai-chen/sql/blob/window-function-poc/integ-test/src/test/resources/correctness/queries/window.txt

Documentation: (Note that you need to enable the new SQL engine to try out this feature: https://github.com/opendistro-for-elasticsearch/sql/blob/master/docs/user/admin/settings.rst#opendistro-sql-engine-new-enabled)

1. Ranking functions: https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/user/dql/window.rst
2. Limitations: https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/user/limitations/limitations.rst

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[penghuo]

Thanks for the change.