Add and use reloadWithReason to iOS

Summary:
This diff adds a new reloading method reloadWithReason that allows callers to provide a reason for why a reload was requested.

This reason is useful for understanding why users are reloading, and why Fast Refresh is bailing out to a full reload. I also updated the places we reload with the reasons listed below.

**Standard native reasons:**
- Redbox
- Command
- Global hotkey
- Profiling controls
- Dev menu - reload
- Dev menu - reset to default
- Dev menu - apply changes

**From JavaScript (added in a later diff):**
- Fast Refresh - Unrecoverable
- Fast Refresh - No root boundary
- Fast Refresh - Invalidated boundary
- Fast Refresh - Invalidated root boundary

**Misc reasons and fallback for when a reason is unavailable:**
- Unknown from JS
- Uncategorized from JS
- Unknown from bridge
- Unknown from cxx bridge
- Requested from bridge
- Custom executor class reset

Reviewed By: cpojer

Differential Revision: D17499339

fbshipit-source-id: 12a21ffa05708c9b921d93911f190cdffc5c78d5

React/Base/RCTBridge.h

@@ -254,12 +254,17 @@ RCT_EXTERN void RCTEnableTurboModule(BOOL enabled);
 /**
  * Reload the bundle and reset executor & modules. Safe to call from any thread.
  */
-- (void)reload;
+- (void)reload __deprecated_msg("Call reloadWithReason instead");
+
+/**
+ * Reload the bundle and reset executor & modules. Safe to call from any thread.
+ */
+- (void)reloadWithReason:(NSString *)reason;
 
 /**
  * Inform the bridge, and anything subscribing to it, that it should reload.
  */
-- (void)requestReload __deprecated_msg("Call reload instead");
+- (void)requestReload __deprecated_msg("Call reloadWithReason instead");
 
 /**
  * Says whether bridge has started receiving calls from javascript.

React/Base/RCTBridge.m

@@ -244,7 +244,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
 
 - (void)didReceiveReloadCommand
 {
-  [self reload];
+  [self reloadWithReason:@"Command"];
 }
 
 - (NSArray<Class> *)moduleClasses
@@ -290,14 +290,22 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
   return [self.batchedBridge moduleIsInitialized:moduleClass];
 }
 
+/**
+ * Legacy reload, please use reloadWithReason and provide a reason for stats.
+ */
 - (void)reload
+{
+   [self reloadWithReason:@"Unknown from bridge"];
+}
+
+- (void)reloadWithReason:(NSString *)reason
 {
   #if RCT_ENABLE_INSPECTOR && !TARGET_OS_UIKITFORMAC
   // Disable debugger to resume the JsVM & avoid thread locks while reloading
   [RCTInspectorDevServerHelper disableDebugger];
   #endif
 
-  [[NSNotificationCenter defaultCenter] postNotificationName:RCTBridgeWillReloadNotification object:self];
+  [[NSNotificationCenter defaultCenter] postNotificationName:RCTBridgeWillReloadNotification object:self userInfo:@{@"reason": reason} ];
 
   /**
    * Any thread
@@ -314,7 +322,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
 
 - (void)requestReload
 {
-  [self reload];
+  [self reloadWithReason:@"Requested from bridge"];
 }
 
 - (Class)bridgeClass