Make sure that hermes-engine is updated with cocoapods. (#37148)

Summary:
Pull Request resolved: #37148

This should fix https://github.com/facebook/react-native/issue/36945, which is also causing annoyance when doing the releases

## Changelog:
[iOS][Changed] - Use contents of sdks/.hermesversion to let cocoapods recognize Hermes updates.

Differential Revision: D45394241

fbshipit-source-id: 3304a7fbcd6303bd22cd7f0c0ce6a3bc2c13cb65

Author: dmytrorykun

packages/react-native/scripts/cocoapods/jsengine.rb

@@ -30,7 +30,11 @@ def setup_hermes!(react_native_path: "../node_modules/react-native", fabric_enab
     abort unless prep_status == 0
 
     pod 'React-jsi', :path => "#{react_native_path}/ReactCommon/jsi"
-    pod 'hermes-engine', :podspec => "#{react_native_path}/sdks/hermes/hermes-engine.podspec"
+    # This `:tag => hermestag` below is only to tell CocoaPods to update hermes-engine when React Native version changes.
+    # We have custom logic to compute the source for hermes-engine. See sdks/hermes-engine/*
+    hermestag_file = File.join(react_native_path, "sdks", ".hermesversion")
+    hermestag = File.exist?(hermestag_file) ? File.read().strip : ''
+    pod 'hermes-engine', :podspec => "#{react_native_path}/sdks/hermes-engine/hermes-engine.podspec", :tag => hermestag
     pod 'React-hermes', :path => "#{react_native_path}/ReactCommon/hermes"
     pod 'libevent', '~> 2.1.12'
 end