Support for vetur specific ts/jsconfig

This commit adds support for a vetur specific tsconfig/jsconfig.

To improve performance on vetur on vue files, the number of files
being processed needs to be minimized. For instance, test.ts files
and mocks can be excluded when editing vue files since these files
should never be accessed by production code.

To use this feature, just place an overriden config files at the
same place as the original config file. The file should have the
suffix vetur, i.e. vetur-tsconfig.json. By using the extends
parameter, the original config file can be included to avoid
duplicate configuration:

{
  "extends": "./tsconfig",
  "exclude": [
    "**/*.test.ts",
    "**/__mocks__/*"
  ]
}

server/src/services/typescriptService/serviceHost.ts

@@ -430,12 +430,15 @@ function inferIsUsingOldVueVersion(tsModule: T_TypeScript, workspacePath: string
 }
 
 function getParsedConfig(tsModule: T_TypeScript, workspacePath: string) {
-  const configFilename =
-    tsModule.findConfigFile(workspacePath, tsModule.sys.fileExists, 'tsconfig.json') ||
-    tsModule.findConfigFile(workspacePath, tsModule.sys.fileExists, 'jsconfig.json');
-  const configJson = (configFilename && tsModule.readConfigFile(configFilename, tsModule.sys.readFile).config) || {
+  const defaultConfig = {
     exclude: defaultIgnorePatterns(tsModule, workspacePath)
   };
+  const configFilenames = ['vetur-tsconfig.json','vetur-jsconfig.json', 'tsconfig.json','jsconfig.json'];
+
+  const configFilename = configFilenames.map(filename => tsModule.findConfigFile(workspacePath, tsModule.sys.fileExists, filename)).find(foundFile => !!foundFile);
+  logger.logDebug(configFilename ? `Using configuration file ${configFilename}` : 'Using default configuration');
+  const configJson = configFilename ? tsModule.readConfigFile(configFilename, tsModule.sys.readFile).config : defaultConfig;
+
   // existingOptions should be empty since it always takes priority
   return tsModule.parseJsonConfigFileContent(
     configJson,