Turbopack: use inline sourcemaps for HMR chunks (#7104)
Previously, we sent a URL with a query string identifying the module,
but this never worked in nextturbo. Instead, this sends the source map
string itself, where it is then encoded as base64 and used inline in the
`eval`ed code.
Test Plan: Updated a client component and verified browser devtools
shows updated source code through the source map.
Closes PACK-2296
