Extract lerp to a separate file

GitOrigin-RevId: 1f60b9dd437006cd2cd9050e12ef7894e3041903

Author: stepankuzmin

src/style-spec/util/color.ts

@@ -1,5 +1,5 @@
 import {parseCSSColor} from 'csscolorparser';
-import {number as lerp} from './interpolate';
+import {number as lerp} from './lerp';
 
 import type {LUT} from '../types/lut';
 

src/style-spec/util/interpolate.ts

@@ -1,8 +1,7 @@
 import Color from './color';
+import {number} from './lerp';
 
-export function number(a: number, b: number, t: number): number {
-    return (a * (1 - t)) + (b * t);
-}
+export {number};
 
 export function color(from: Color, to: Color, t: number): Color {
     return new Color(

src/style-spec/util/lerp.ts

@@ -0,0 +1,3 @@
+export function number(a: number, b: number, t: number): number {
+    return (a * (1 - t)) + (b * t);
+}

tsconfig.strictNullChecks.json

@@ -68,6 +68,7 @@
     "./src/util/throttle.ts",
     "./src/util/throttled_invoker.ts",
     "./src/util/worker_class.ts",
-    "./src/style-spec/deref.ts"
+    "./src/style-spec/deref.ts",
+    "./src/style-spec/util/lerp.ts"
   ]
 }