Add SymbolPlacement options of 'justEnd' and 'justBegin' to work similarly to the CIMSymbol options for ExtremityPlacement

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## Motivation

I want to be able to position a symbol at the end of a line. Like an arrow, or x-marks-the-spot, so users can easily understand where a ployline beings and ends.

## Design Alternatives

Right now, as the data I am using is not under my team's control, we need to make a 2nd call to fetch both vector and GeoJSON data and then create a second layer that places the end points using the GeoJSON. I know you can add things along the line, but that can create unnecessary clutter.

## Design

I think it should work like CIMSymbol's ExtremityPlacement, with SymbolPlacement having a justEnd and justBegin option. The symbol would default rotation to align with the line at the point of placement.

### Mock-Up

'symbol-placement': 'justEnd '

### Concepts

'symbol-placement' would get 2 new options

Start by locating the SymbolPlacement implementation and the CIMSymbol ExtremityPlacement behavior referenced in the issue. Determine how the proposed justEnd and justBegin options should affect placement and line-aligned rotation, then verify the symbol-placement behavior with the project's existing rendering tests. Done means both options are supported without requiring a second data call or layer.

Written by the indexing model from the issue text.