Add redbox subspec to React-debug pod (#56584)

Add a "redbox" subspec to React-debug.podspec with its own header_dir,
following the same pattern React-Fabric uses for its subdirectories.
Without this, static library builds (without USE_FRAMEWORKS) flatten all
headers into the top-level header_dir ("react/debug"), so imports like
`<react/debug/redbox/RedBoxErrorParser.h>` fail because the "redbox/"
subdirectory is lost.

Author: motiz88

packages/react-native/ReactCommon/react/debug/React-debug.podspec

@@ -25,11 +25,16 @@ Pod::Spec.new do |s|
 s.author="Meta Platforms, Inc. and its affiliates"
 s.platforms=min_supported_versions
 s.source=source
-s.source_files=podspec_sources("**/*.{cpp,h}","**/*.h")
-s.exclude_files="**/tests/**/*.{cpp,h}"
+s.source_files=podspec_sources("*.{cpp,h}","*.h")
 s.header_dir="react/debug"
 s.pod_target_xcconfig={"CLANG_CXX_LANGUAGE_STANDARD"=>rct_cxx_language_standard(),
 "DEFINES_MODULE"=>"YES"}
 
 resolve_use_frameworks(s,header_mappings_dir: "../..",module_name: "React_debug")
+
+s.subspec"redbox"do |ss|
+ss.source_files=podspec_sources("redbox/*.{cpp,h}","redbox/*.h")
+ss.exclude_files="redbox/tests/**/*.{cpp,h}"
+ss.header_dir="react/debug/redbox"
+end
 end