Make separate private constructor for Resolver

Author: liamappelbe

bin/format_coverage.dart

@@ -79,7 +79,7 @@ Future<void> main(List<String> arguments) async {
   String output;
   final resolver = env.bazel
       ? BazelResolver(workspacePath: env.bazelWorkspace)
-      : Resolver(
+      : await Resolver.create(
           packagesPath: env.packagesPath,
           packagePath: env.packagePath,
           sdkRoot: env.sdkRoot,

lib/src/resolver.dart

@@ -9,7 +9,12 @@ import 'package:path/path.dart' as p;
 
 /// [Resolver] resolves imports with respect to a given environment.
 class Resolver {
-  Resolver(
+  @Deprecated('Use Resolver.create')
+  Resolver({this.packagesPath, this.sdkRoot})
+      : _packages = packagesPath != null ? _parsePackages(packagesPath) : null,
+        packagePath = null;
+
+  Resolver._(
       {this.packagesPath,
       this.packagePath,
       this.sdkRoot,
@@ -21,7 +26,7 @@ class Resolver {
     String? packagePath,
     String? sdkRoot,
   }) async {
-    return Resolver(
+    return Resolver._(
       packagesPath: packagesPath,
       packagePath: packagePath,
       sdkRoot: sdkRoot,