Add missing Functionality in MaterializedViewQueryToolChest

[ritik02]

Add postMergeQueryDecoration() for TopN Queries and decorateObjectMapper() for GroupBy Queries in MaterializedViewQueryToolChest .

Description

1. MaterializedViewQueryToolChest did not implement postMergeQueryDecoration() for TopN Queries hence not returning expected results . As without postMergeQueryDecoration() , each segment returns only topN results instead of max(topN,1000) hence after merging , results are not as expected.
2. MaterializedViewQueryToolChest did not implement decorateObjectMapper() for GroupBy Queries hence returning ArrayBasedResults whereas expected is MapBasedResults.

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This PR has:

• been self-reviewed.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths.
• been tested in a test Druid cluster.

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Key changed/added classes in this PR

• MaterializedViewQueryQueryToolChest
• MaterializedViewQueryQueryToolChestTest

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 4 weeks if no further activity occurs. If you think that's incorrect or this pull request should instead be reviewed, please simply write any comment. Even if closed, you can still revive the PR at any time or discuss it on the dev@druid.apache.org list. Thank you for your contributions.

[ritik02]

@jihoonson

[stale]

This issue is no longer marked as stale.

[ritik02]

@zhangxinyu1

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 4 weeks if no further activity occurs. If you think that's incorrect or this pull request should instead be reviewed, please simply write any comment. Even if closed, you can still revive the PR at any time or discuss it on the dev@druid.apache.org list. Thank you for your contributions.

[stale]

This pull request/issue has been closed due to lack of activity. If you think that is incorrect, or the pull request requires review, you can revive the PR at any time.

[ritik02]

Can anyone look into this pull request . Materialized views are being used by a lot people and it gives incorrect query results , ive resolved this .

[abhishekagarwal87]

LGTM