feat: system for compile feature flags

[jackgerrits]

Compile features are optional parts of the library or just optional features. This PR organizes them into a consistent system.

# We control library features with the feature list, including conditional
# compilation or optional parts.
#
# This feature list can be specified by:
#   - Specifying individual features with -DVW_FEAT_FEAT1=ON/OFF
#
# This allows us to enable/disable features without changing the code
# If a feature called X is enabled then:
#   - The cmake variable VW_FEAT_X is set to ON, otherwise it is OFF
#   - The C++ macro VW_FEAT_X_ENABLED is defined if the feature is enabled, otherwise it is not defined
#
# Features:
#   FLATBUFFERS: Enable flatbuffers support
#   CSV: Enable csv parser
#   LAS_SIMD: Enable large action space with explicit simd (only work with linux for now)

[lalo]

is there some sort of 'default' enabled collection or it depends if the flags are defaulted on or off?

[jackgerrits]

There is a default list at the top of the VowpalWabbitFeatures.cmake file

[jackgerrits]

Scaled it back to just include the "framework"