Type-safe project accessors are not regenerated when new projects are added to the build

[alllex]

There is no minimal reproducer for this, but it has been observed in the gradle/gradle build at the very least.
However, this is a general project accessor bug.

A compilation error in a Kotlin build script hints that the accessor is not there:

Script compilation error:

  Line 30:     api(projects.serviceLookup)
                            ^ Unresolved reference: serviceLookup

However, the given project was already added in settings, and script compilation was trying to run against the stale version of accessors.