fix: Downlevel type definitions (#410)

The definitions are now made compatible with older versions of typescript
adds a build step using downlevel-dts to handle this

NODE-2844

package.json

@@ -38,6 +38,7 @@
     "@typescript-eslint/parser": "^3.10.1",
     "benchmark": "^2.1.4",
     "chai": "^4.2.0",
+    "downlevel-dts": "^0.7.0",
     "eslint": "^7.7.0",
     "eslint-config-prettier": "^6.11.0",
     "eslint-plugin-prettier": "^3.1.4",
@@ -81,7 +82,7 @@
     "test-node": "mocha test/node",
     "test-browser": "karma start karma.conf.js",
     "build:ts": "tsc",
-    "build:dts": "npm run build:ts && api-extractor run --typescript-compiler-folder node_modules/typescript --local && rimraf 'lib/**/*.d.ts*'",
+    "build:dts": "npm run build:ts && api-extractor run --typescript-compiler-folder node_modules/typescript --local && rimraf 'lib/**/*.d.ts*' && downlevel-dts bson.d.ts bson.d.ts",
     "build:bundle": "rollup -c rollup.config.js",
     "build": "npm run build:dts && npm run build:bundle",
     "lint": "eslint -v && eslint --ext '.js,.ts' --max-warnings=0 src test && tsc -v && tsc --noEmit",

src/long.ts

@@ -291,7 +291,8 @@ export class Long {
   /**
    * Tests if the specified object is a Long.
    */
-  static isLong(value: unknown): value is Long {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/explicit-module-boundary-types
+  static isLong(value: any): value is Long {
     return isObjectLike(value) && value['__isLong__'] === true;
   }