Fix issue with "File name X differs from already included" on Windows

On Sublime Text (and potentially other clients) the paths passed to
LSP servers on Windows have upper-case drive letter. So either:
 - C:\folder\foo
 or
 - file:///C:/folder/foo

This is problematic with Vetur as it normalizes URI paths received from
the client in notifications and requests like "textDocument/completion",
"textDocument/didChange" etc. It uses getFileFsPath() utility path to
get filesystem path from the URI.

But it doesn't do normalization for the filesystem path received through
"InitializeParams.rootPath" and then uses that path to initialize the
Typescript server. That list (parsedConfig.fileNames in serviceHost.ts)
is later used to lookup files passed through other calls and causes
issues due to there being duplicate path differing only with drive letter.

This issue doesn't reproduce in VSCode as it itself normalizes paths
passed to the server and automatically lower-cases the drive letter.

Fix by normalizing the path passed through InitializeParams.rootPath.

Fixes vuejs#2433

server/src/services/vls.ts

@@ -1,5 +1,5 @@
 import * as path from 'path';
-import { getFileFsPath } from '../utils/paths';
+import { getFileFsPath, normalizeFileNameToFsPath } from '../utils/paths';
 
 import {
   DidChangeConfigurationParams,
@@ -104,13 +104,17 @@ export class VLS {
       };
     }
 
-    this.workspacePath = workspacePath;
+    this.workspacePath = normalizeFileNameToFsPath(workspacePath);
 
     this.vueInfoService.init(this.languageModes);
-    await this.dependencyService.init(workspacePath, config.vetur.useWorkspaceDependencies, config.typescript.tsdk);
+    await this.dependencyService.init(
+      this.workspacePath,
+      config.vetur.useWorkspaceDependencies,
+      config.typescript.tsdk
+    );
 
     await this.languageModes.init(
-      workspacePath,
+      this.workspacePath,
       {
         infoService: this.vueInfoService,
         dependencyService: this.dependencyService