docs - filters

[nllho]

Super gnarly topic... so many dependencies!

Main changes:

• Filters troubleshooting: consolidated info with docs.
• Data reference: moved out of SQL section and brought up to date (it's a great resource for data types, which is the root cause of many issues, filters or otherwise).
• SQL: updated info on field filters and troubleshooting.

These changes break some links in Learn. I've got them noted down -- will follow up when the 45 docs go out.

Gonna take one more pass just to look at formatting tomorrow, but otherwise this is ready for review.