Fix for 17497 (#17498)

Summary:
Changed runAndroid.js to generate .packager.bat and launchPackager.ba…t to call it to setup the environment variable

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Trying to use react-native on a Windows box with a virus killer that runs on port 8081...

(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)
1) Start an android emulator
2) on a react-native project (with the changes), run `react-native run-android --port 9988`.
3) When the packager starts, verify that it states the correct port in the terminal window.
4) verify that the application correctly starts in the Emulator.

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/react-native-website, and link to your PR here.)

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
[INTERNAL] [BUGFIX] [./scripts] - Fixed runAndroid to enable the use of a package on port <> 8081 for Windows.
Closes #17498

Differential Revision: D8682067

Pulled By: hramos

fbshipit-source-id: 6604b827077b3a6a2da9914c1fd36dad6ef30e43

Author: ihenshaw

local-cli/runAndroid/runAndroid.js

@@ -349,25 +349,35 @@ function runOnAllDevices(
 }
 
 function startServerInNewWindow(port) {
-  const scriptFile = /^win/.test(process.platform)
+  // set up OS-specific filenames and commands
+  const isWindows = /^win/.test(process.platform);
+  const scriptFile = isWindows
     ? 'launchPackager.bat'
     : 'launchPackager.command';
+  const packagerEnvFilename = isWindows
+    ? '.packager.bat'
+    : '.packager.env';
+  const portExportContent = isWindows
+    ? `set RCT_METRO_PORT=${port}`
+    : `export RCT_METRO_PORT=${port}`;
+
+  // set up the launchpackager.(command|bat) file
   const scriptsDir = path.resolve(__dirname, '..', '..', 'scripts');
   const launchPackagerScript = path.resolve(scriptsDir, scriptFile);
   const procConfig = {cwd: scriptsDir};
   const terminal = process.env.REACT_TERMINAL;
 
-  // setup the .packager.env file to ensure the packager starts on the right port
+  // set up the .packager.(env|bat) file to ensure the packager starts on the right port
   const packagerEnvFile = path.join(
     __dirname,
     '..',
     '..',
     'scripts',
-    '.packager.env',
+    packagerEnvFilename
   );
-  const content = `export RCT_METRO_PORT=${port}`;
+  
   // ensure we overwrite file by passing the 'w' flag
-  fs.writeFileSync(packagerEnvFile, content, {encoding: 'utf8', flag: 'w'});
+  fs.writeFileSync(packagerEnvFile, portExportContent, {encoding: 'utf8', flag: 'w'});
 
   if (process.platform === 'darwin') {
     if (terminal) {

scripts/launchPackager.bat

@@ -5,6 +5,7 @@
 
 @echo off
 title Metro Bundler
+call .packager.bat
 node "%~dp0..\local-cli\cli.js" start
 pause
 exit