Move JSCRuntime into its own folder (#35482)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/35482

This change moves the JSCRuntime.h/cpp into a `jsc` folder.

This change is required for several reasons:
1. on iOS, the new `jsi`, `jsidynamic` and `jsc` setup is breaking the `use_frameworks!` with  `:linkage => :static` option with the old architecture. So it is a regression.
2. JSCRuntime is required by some libraries and needs to be exposed as a prefab and the current setup makes it hard to achieve.

allow-large-files

## Changelog:
[General][Changed] - Move JSCRuntime into a separate pod/prefab

Reviewed By: cortinico

Differential Revision: D41533778

fbshipit-source-id: 642240c93a6c124280430d4f196049cb67cb130b

ReactAndroid/src/main/jni/react/jscexecutor/BUCK

@@ -16,7 +16,7 @@ rn_xplat_cxx_library(
     deps = [
         FBJNI_TARGET,
         react_native_target("jni/react/jni:jni"),
-        react_native_xplat_target("jsi:JSCRuntime"),
+        react_native_xplat_target("jsc:JSCRuntime"),
         react_native_xplat_target("jsiexecutor:jsiexecutor"),
     ],
 )

ReactAndroid/src/main/jni/react/jscexecutor/OnLoad.cpp

@@ -6,7 +6,7 @@
  */
 
 #include <fbjni/fbjni.h>
-#include <jsi/JSCRuntime.h>
+#include <jsc/JSCRuntime.h>
 #include <jsireact/JSIExecutor.h>
 #include <react/jni/JReactMarker.h>
 #include <react/jni/JSLogging.h>