add stereographic projection

Author: birkskyum

src/reference/v8.json

@@ -4575,10 +4575,13 @@
       "default": "mercator",
       "values": {
         "mercator": {
-          "doc": "The Mercator projection."
+          "doc": "Web Mercator projection."
         },
         "globe": {
-          "doc": "The globe projection."
+          "doc": "Globe projection. Adaptive transition from Stereographic to Mercator."
+        },
+        "stereographic": {
+          "doc": "Stereographic projection."
         }
       }
     }

src/validate/validate_projection.test.ts

@@ -26,7 +26,7 @@ describe('Validate projection', () => {
     test('Should return errors according to spec violations', () => {
         const errors = validateProjection({validateSpec, value: {type: 1 as any}, styleSpec: v8, style: {} as any});
         expect(errors).toHaveLength(1);
-        expect(errors[0].message).toBe('type: expected one of [mercator, globe], 1 found');
+        expect(errors[0].message).toBe('type: expected one of [mercator, globe, stereographic], 1 found');
     });
 
     test('Should pass if everything is according to spec', () => {