fix issue with nested virtual column index supplier for partial paths when processing from raw

[clintropolis]

Description

Fixes an issue when filtering NestedFieldVirtualColumn using 'processFromRaw' (e.g. JSON_QUERY instead of JSON_VALUE) when using partial paths. NestedFieldVirtualColumn was incorrectly returning null from getIndexSupplier in this case instead of NoIndexesColumnIndexSupplier.getInstance() to instruct the processing to fall back to using value matchers. Added test case for this, as well as another similar case which was working correctly where it should also fall back to using no-indexes when referring to an array element, to ensure no future regressions.

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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, ensuring the threshold for code coverage is met.
• been tested in a test Druid cluster.