Avoid ReDOS on table paste

[theinterned]

Resolves https://github.com/github/primer/issues/2532

This came in from a support escalation: it is possible to create a ReDOS crash on paste of a table with a (fairly contrived) clipboard contents. Thanks @P0cas for reporting this!

The crash is due to a Catastrophic Backtracking regex in the table plugin, which is triggered by the following clipboard contents:

example.oncopy = e => {
  e.preventDefault()
  const badTable = '<table'.repeat(99999) + '<div><table></div>'
  e.clipboardData.setData('text/html', badTable)
}

While the problem is contrived the fix is fairly simple: rather than use a regex to insert the formatted table, we can just splice it in directly.

[primer-css]

👋 Hello and thanks for pinging us! This issue or PR has been added to our inbox and a Primer first responder will review it soon.

• 🎨 If this is a PR that includes a visual change, please make sure to add screenshots in the description or deploy this code to a lab machine with instructions for how to test.
• ⏩ If this is a PR that includes changes to an interaction, please include a video recording in the description.
• ⚠️ If this is urgent, please visit us in #primer on Slack and tag the first responders listed in the channel topic.

[joshblack]

Thanks for fixing this! 🙌

[P0cas]

thanks 😊