fix(react-router-v3): makes normalizeTransactionName take a callback function

[scefali]

This PR converts the normalizeTransactionName to a function that takes a callback instead of returning a value. This is to fix a bug where normalizeTransactionName returns a value before the callback passed to match is called. In that case, we end up returning the wrong value and the transaction name is incorrect. We see this in Sentry where we get a transaction for /settings/sentry/integrations/ instead of /settings/:orgId/integrations/. This happens because the callback passed to match might be called asynchronously (https://github.com/ReactTraining/react-router/blob/42fe32d8f4ebec170a6d980badbc702ab88b5897/modules/matchRoutes.js#L249). So we need a callback here as well to get the proper behavior.

I tried to test this with Sentry but I think version 5.25.0-beta.2 introduces some breaking changes compared to 5.24.2 which is what we currently use.

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	18.01 KB (0%)
@sentry/browser - Webpack	18.82 KB (0%)
@sentry/react - Webpack	18.82 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	23.81 KB (0%)

[lobsterkatie]

LGTM!