Add support for property queries.

[greenrobot-team]

Squashed and rebased changes from #75

Remaining issues

• See Help required: query property #75 for remaining issues.
  • .find(replaceNullWith:-1) broken for negative values: it looks like unsigned integers are returned? E.g. 255/65535/4294967295/-1 is returned instead of -1 for 8/16/32/64 bit integers. Wrong types in Structs.
  • Byte unsigned issue is rooted in the binding treating them as unsigned, submitted patch in Unmarshal byte as Int8 (was Uint8). #109.
  • Similar: floats return 0.0 instead of replacement value, but double works fine. Was casting double to float.
• There are code errors in bindings.dart and signatures.dart.
• Native property query appears to auto-close/free, e.g. getting results twice crashes, or closing/freeing the property query crashes. Gone, probably wrong pointer types? Odd.
• Missing from tests: edge cases (e.g. min/max integer, NaN float, etc.).

[greenrobot-team]

@vaind Two other issues: it looks like for 8-32 bit integers, if their value is negative the property query returns an unsigned value. When doing sums or average they also appear to be treated as unsigned.

Secondly, byte values appear to get returned as unsigned, even via the box interface. Though the property query sum then works correctly. Oh my.

[greenrobot-team]

Resolved integer issue by correcting Structs of int array types to use signed integer pointers.

[greenrobot-team]

Byte unsigned issue is rooted in the binding treating them as unsigned, submitted patch in #109.

This leaves one issue: null floats (not doubles) getting returned as 0.0.

[greenrobot-team]

Was casting double to float, issue resolved as well.

Pending #109 and a final round of clean-up and docs (e.g. on find(), sum() and etc. methods).

[vaind]

@greenrobot-team see the latest commits - should be ready for the merge after #109 is merged so that the tests pass

[vaind]

Just for future reference - the issue with double-free/invalid pointers was caused by a signature mismatch between dart property query function definitions and c-api functions, e.g. obx_query_prop_sum - it was missing the last argument...

[greenrobot-team]

Rebased onto main with #109 included. Tests all good now. Merging.