Make tsconfig.json selection during webpack deterministic.

Without this `configFile` option, ts-loader apparently does not
guarantee a deterministic choice of which of the three `tsconfig.json`
files below `extensions/ql-vscode` actually gets used during webpack.
This leads to very strange behavior as even removing dead code can
change which `tsconfig.json` 'wins the race'. I observed that removing
a dependence on `semmle-bqrs` from `src/view` *tended* to make
`ts-loader` choose `src/compare/view/tsconfig.json` instead.

Author: jcreedcmu

extensions/ql-vscode/gulpfile.js/webpack.config.ts

@@ -20,6 +20,9 @@ export const config: webpack.Configuration = {
       {
         test: /\.(ts|tsx)$/,
         loader: 'ts-loader',
+        options: {
+          configFile: 'view/tsconfig.json',
+        }
       },
       {
         test: /\.less$/,