[jira] [Created] (FLINK-11822) Introduce Flink metadata handler

[Shang Yuanchun (Jira)]

godfrey he created FLINK-11822:
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             Summary: Introduce Flink metadata handler
                 Key: FLINK-11822
                 URL: https://issues.apache.org/jira/browse/FLINK-11822
             Project: Flink
          Issue Type: New Feature
          Components: API / Table SQL
            Reporter: godfrey he
            Assignee: godfrey he


Calcite has defined various metadata handlers(e.g. `RowCount`, `Selectivity`) and provided default implementation(e.g. `RelMdRowCount`, `RelMdSelectivity`). However, the default implementation can't completely meet our requirements, e.g. some of its logic is incomplete，and some `RelNode`s  are not considered.
There are two options to meet our requirements:
option 1. Extends from default implementation, overrides method to improve its logic, add new methods for new `RelNode`. The advantage of this option is we just need to focus on the additions and modifications. However, its shortcomings are also obvious: we have no control over the code of non-override methods in default implementation classes especially when upgrading the Calcite version.
option 2. Extends from metadata handler interfaces, reimplement all the logic. Its shortcomings are very obvious, however we can control all the code logic that's what we want.

so we choose option 2!

In this jira, only basic metadata handles will be introduce, including:
`FlinkRelMdPercentageOriginalRow`,
`FlinkRelMdNonCumulativeCost`,
`FlinkRelMdCumulativeCost`,
`FlinkRelMdRowCount`,
`FlinkRelMdSize`,
`FlinkRelMdSelectivity`,
`FlinkRelMdDistinctRowCoun`,
`FlinkRelMdPopulationSize`,
`FlinkRelMdColumnUniqueness`,
`FlinkRelMdUniqueKeys`




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