Update various parts of DevTools to account for the fact that the global "hook" might be undefined if DevTools didn't inject it (due to the page's `contentType`) it (due to the page's `contentType`)
* Updated DevTools local development instructions to mention experimental build step
* Added a command to download latest experimental release (for DevTools)
* Updated build instructions for clarity
* Added build-for-devtools package alias
* Added rudimentary context menu hook and menu UI
* Added backend support for copying a value at a specific path for the inspected element
* Added backend support for storing a value (at a specified path) as a global variable
* Added special casing to enable copying undefined/unserializable values to the clipboard
* Added copy and store-as-global context menu options to selected element props panel
* Store global variables separately, with auto-incremented name (like browsers do)
* Added tests for new copy and store-as-global backend functions
* Fixed some ownerDocument/contentWindow edge cases
* Refactored context menu to support dynamic options
Used this mechanism to add a conditional menu option for inspecting the current value (if it's a function)
* Renamed "safeSerialize" to "serializeToString" and added inline comment
PR #16752 changed how we were injecting the backend script to be done by the content script in order to work around Trusted Type limitations with our previous approach. This may have caused a regression (see #16840) so I'm backing it out to verify.
* Correct link for troubleshooting react-dev-tools (#16690)
As pointed out in #16690 - the link for 'React Tab Doesn't Show Up' points to the empty README.MD.
This points it to that section in the v3 version README.MD - until an updated section will be added to the new dev-tools.
* Add a "The React Tab Doesn't Show Up" section
Add the troubleshooting section to the react dev tools readme
* point to the correct section in react-dev-tools readme
After adding the troubleshooting section to the readme - this will point to the correct place
* Moved README file to GitHub
* Update new issue link to include DevTools label
Brian Vaughn