Add STAC API Filter Extension (CQL2) support

[matthewhanson]

• STAC API 1.0.0-beta.5 Filter Extension: https://github.com/radiantearth/stac-api-spec/tree/v1.0.0-beta.5/fragments/filter
• OGC CQL2 spec: https://github.com/opengeospatial/ogcapi-features/tree/master/cql2
• CQL-Text BNF: https://github.com/opengeospatial/ogcapi-features/blob/master/cql2/standard/schema/cql2.bnf
• CQL-JSON JSON Schema: https://github.com/opengeospatial/ogcapi-features/blob/master/cql2/standard/schema/cql2.json

The conformance classes Basic CQL2 and Basic Spatial Operators should be implemented. Basic CQL2 allows the logical operators (AND, OR, NOT), comparison operators (=, <>, <, <=, >, >=), and IS NULL against string, numeric, boolean, date, and datetime types. Basic Spatial Operators allows S_INTERSECTS (spatial intersects) on geometry fields.

Stretch: Advanced Comparison Operators defines the LIKE, BETWEEN, and IN operators, though BETWEEN and IN can be be written less-concisely using comparisons AND'ed or OR'ed together. LIKE cannot (practically) be worked-around this way.

Other implementations:

• pgstac - most up-to-date one
• Pygeoap - might be out of date wrt the latest spec

Open Questions:

• CQL2-Text and/or CQL2-JSON?
• which conformance classes?

[demiurg]

Relevant links:
OGC Issues: https://github.com/opengeospatial/ogcapi-features/issues?q=is%3Aissue+is%3Aopen+label%3A%22CQL+Grammar%22
OGC "Spec": https://portal.ogc.org/files/96288#cql-core
CQL-JSON notes: opengeospatial/ogcapi-features#575
Simple CQL: opengeospatial/ogcapi-features#579
^ no other spec
Examples: https://github.com/opengeospatial/ogcapi-features/tree/master/extensions/cql/standard/schema/examples
CQL BNF: https://github.com/geotools/geotools/blob/main/modules/library/cql/CQL.md

Library found for CQL-TEXT parsing and further extending (MIT):
https://www.npmjs.com/package/sql-where-parser
https://github.com/shaunpersad/sql-where-parser/blob/master/SqlWhereParser.js