Pass Metro's own @babel/runtime to Babel presets

[robhogan]

8388f71 added the metro: scheme resolver, which maps metro:babel-runtime/<path> to metro-runtime's own @babel/runtime. This is the Metro half of pointing @babel/plugin-transform-runtime at it - the preset half is react/react-native#57974, and until a preset reads it this is a no-op.

When transformer.enableBabelRuntime is true (the default), Metro now passes presets babelRuntimeModuleName: 'metro:babel-runtime' and that copy's installed version as Babel caller data, matching what @react-native/babel-preset reads. Caller data reaches a preset however it's configured, including from a project babel.config.js. The version is read from the installed package, so its package.json joins the transform cache key.

A string enableBabelRuntime (a version of the project's own @babel/runtime) keeps its meaning and passes neither. It's now documented as deprecated.

With presets importing from it, Metro's @babel/runtime needs to be in the file map, and Metro adds it as a root at startup when no configured root contains it. If that fails (eg the watcher can't watch it), Metro now warns and starts anyway, rather than failing for projects that never import from it.

Changelog:

 - **[Feature]**: When `transformer.enableBabelRuntime` is `true`, pass Metro's own `@babel/runtime` (`metro:babel-runtime`) and its installed version to Babel presets via caller data
 - **[Deprecated]**: String values of `transformer.enableBabelRuntime` (use `true`)

Test plan:
New integration test builds and runs a bundle through the full Metro + Babel pipeline, with a preset that reads the caller data as @react-native/babel-preset does. Its fixture uses import * as, whose helper @babel/runtime only exports from 7.14.0, so the helper is imported rather than inlined only if the version reaches the preset. Covered with enableBabelRuntime both true and false. Metro's @babel/runtime sits outside the test's watch folders, so this also exercises the dynamic root from #2065 end to end.