PoC: Add MQL translation skeleton

[jsflax]

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[coveralls-official[bot]]

Pull Request Test Coverage Report for Build github_pull_request_285284

• 264 of 308 (85.71%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on jf/mql at 91.664%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/realm/util/bson/bson.cpp	6	7	85.71%
src/realm/object-store/results.cpp	0	4	0.0%
src/realm/parser/query_bson.cpp	117	156	75.0%
<!--	Total:	264	308

Totals
Change from base Build 1854:	91.7%
Covered Lines:	231504
Relevant Lines:	252558

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💛 - Coveralls

[jsflax]

Let's not merge this yet.

[jedelbo]

@jsflax What is going to happen with this PR?

[jsflax]

Unclear right now– we need to road map this before moving forward with the actual feature.

However, if this is adding enough additional useful stuff, I'd be fine removing the MQL features from the header and then consider merging the rest.

[jedelbo]

@jsflax you mean removing the changes to results.hpp? I am not sure what the risk of keeping it would be. I would prefer that we can keep the test.