- Do not carry it over everywhere as parameter, it is a shared
instance anyway and the lifecycle is pretty much the app lifecycle
from the moment we instantiate a map.
- Rename to BackgroundScheduler because it is a Scheduler that will
do tasks in the background, we don't make assumptions if it is a
thread pool or a single thread.
- Most importantly, remove the dependency from `core` on `platform`.
Before this change, symbol layer was only checking whether top level
'text-field' layout property expression is FormatExpression and if it
has paint property overrides. This change takes into account that
'text-field' might have nested expressions, thus, requires traversal
over child expressions.
Fixes: #14254
* [core] Add format override expression and formatted section to evaluation context
* [core] Add textColor to TaggedString's formatted section
* [core] Add FormatSectionOverrides and introduce overridable properties
* [core] Populate symbol layer paint properties for text sections
* [core] Add benchmark for style that uses text-color override
* [core] Add unit test for FormatOverrideExpression
* [core] Add unit test for FormatSectionOverrides
`LayerManager` is now responsible for `RenderLayer` instances creation,
so that there is a single entry point for creating of objects, which
correspond to a certain layer type.
The `LayerType type` field is dropped from `Layer::Impl`.
