Workarounds for Yarn not playing nicely on Windows

- Bypass `yarn run` when running on Windows; instead, we can go directly
to `node_modules/.bin/`
- Create batch scripts so users don't need to type in `ruby bin/webpack`
manually

See discussion on rails#583

lib/install/bin/webpack-dev-server.bat.tt

@@ -0,0 +1 @@
+@ruby bin\webpack-dev-server %*

lib/install/bin/webpack-dev-server.tt

@@ -57,8 +57,14 @@ newenv = {
   "ASSET_HOST" => DEV_SERVER_ADDR.shellescape
 }.freeze
 
-cmdline = ["yarn", "run", "webpack-dev-server", "--", "--progress", "--color", "--config",
+if Gem.win_platform?
+  # Workaround for yarn not playing nicely with path separators
+  cmdline = ["#{NODE_MODULES_PATH}/.bin/webpack-dev-server", "--progress", "--color", "--config",
 WEBPACK_CONFIG, "--host", LISTEN_IP_ADDR, "--port", PORT.to_s] + ARGV
+else
+  cmdline = ["yarn", "run", "webpack-dev-server", "--", "--progress", "--color", "--config",
+WEBPACK_CONFIG, "--host", LISTEN_IP_ADDR, "--port", PORT.to_s] + ARGV
+end
 
 Dir.chdir(APP_PATH) do
   exec newenv, *cmdline

lib/install/bin/webpack.bat.tt

@@ -0,0 +1 @@
+@ruby bin\webpack %*

lib/install/bin/webpack.tt

@@ -20,7 +20,12 @@ unless File.exist?(WEBPACK_CONFIG)
 end
 
 newenv  = { "NODE_PATH" => NODE_MODULES_PATH.shellescape }
-cmdline = ["yarn", "run", "webpack", "--", "--config", WEBPACK_CONFIG] + ARGV
+if Gem.win_platform?
+  # Workaround for yarn not playing nicely with path separators
+  cmdline = ["#{NODE_MODULES_PATH}/.bin/webpack", "--config", WEBPACK_CONFIG] + ARGV
+else
+  cmdline = ["yarn", "run", "webpack", "--", "--config", WEBPACK_CONFIG] + ARGV
+end
 
 Dir.chdir(APP_PATH) do
   exec newenv, *cmdline