chore: rename hermes-inspector-msggen to @react-native/hermes-inspector-msggen (#34850)

Summary:
This PR renames ` hermes-inspector-msggen` to `react-native/hermes-inspector-msggen`, moves it to  `packages/hermes-inspector-msggen` and makes the package private  as part of RFC480.

Related to #34692

## Changelog

[General] [Changed] - Move and rename `hermes-inspector-msggen` to `react-native/hermes-inspector-msggen`

Pull Request resolved: #34850

Test Plan: run `sh ReactCommon/hermes/inspector/tools/run_msggen`

Reviewed By: mattbfb

Differential Revision: D40060406

Pulled By: cortinico

fbshipit-source-id: e018fd88e8374a69fbd8737fbb9abe7565d4a003

Author: gabrieldonadel

ReactCommon/hermes/inspector/tools/msggen/yarn.lock

@@ -12,7 +12,7 @@ FBSOURCE=$(hg root)
 CLANG_FORMAT="${FBSOURCE}/tools/third-party/clang-format/clang-format"
 SIGNEDSOURCE="${FBSOURCE}/tools/signedsource"
 
-cd "${DIR}/msggen"
+pushd "../../../../packages/hermes-inspector-msggen"
 
 yarn install
 yarn build
@@ -28,3 +28,5 @@ node bin/index.js \
 
 "${SIGNEDSOURCE}" sign "${HEADER_PATH}"
 "${SIGNEDSOURCE}" sign "${CPP_PATH}"
+
+popd >/dev/null