[Fresh] Add options to configure RefreshReg and RefreshSig identifiers

[vasiliicuhar]

Allow to override $RefreshReg$ and $RefreshSig$ identifiers.
Main reason is to use import.meta in async environments (i.e. rollup + SystemJS) builds instead of relying on globals.

Usage:

{
  "plugins": [
    ["react-refresh/babel", {
      "refreshReg": "import.meta.refreshReg",
      "refreshSig": "import.meta.refreshSig"
    }]
  ]
}

Closes: #17237

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