exact-by-default in xplat/js

Summary:
Turns on the exact-by-default flag in xplat/js and gets rid of the implicit inexact object lint, which has no effect when exact-by-default is on.

Will land this on Monday along with an announcement post.

Changelog: [Internal]

Reviewed By: gkz

Differential Revision: D18863276

fbshipit-source-id: 07a31e957bea1d1e053e8fa5975fdb1b6da1bdc4

.flowconfig

@@ -36,6 +36,8 @@ emoji=true
 esproposal.optional_chaining=enable
 esproposal.nullish_coalescing=enable
 
+exact_by_default=true
+
 module.file_ext=.js
 module.file_ext=.json
 module.file_ext=.ios.js
@@ -72,7 +74,6 @@ inexact-spread=warn
 unnecessary-invariant=warn
 signature-verification-failure=warn
 deprecated-utility=error
-implicit-inexact-object=error
 
 [strict]
 deprecated-type

.flowconfig.android

@@ -36,6 +36,8 @@ emoji=true
 esproposal.optional_chaining=enable
 esproposal.nullish_coalescing=enable
 
+exact_by_default=true
+
 module.file_ext=.js
 module.file_ext=.json
 module.file_ext=.android.js
@@ -72,7 +74,6 @@ inexact-spread=warn
 unnecessary-invariant=warn
 signature-verification-failure=warn
 deprecated-utility=error
-implicit-inexact-object=error
 
 [strict]
 deprecated-type

jest/preprocessor.js

@@ -40,6 +40,8 @@ module.exports = {
       }).code;
     }
 
+    /* $FlowFixMe(>=0.99.0 site=react_native_fb) This fixme can be removed after metro releases
+     * 0.58 and RN upgrades its dependency */
     const {ast} = transformer.transform({
       filename: file,
       options: {