Documentation lacks method signatures

[1ec5]

Generating the published documentation for v2.8.0-beta.3 produces a slew of warnings about missing USRs. This causes the generated pages to lack method signatures, and anchors to specific sections of the pages are broken. The warnings start out with something about conflicts:

Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: instance method calculate(_:completionHandler:), instance method calculate(_:completionHandler:)
Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: type alias LocationSpeed, type alias LocationSpeed
Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: type alias LocationAccuracy, type alias LocationAccuracy
Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: type alias Color, type alias Color, structure Color
Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: type alias Scale, type alias Scale
Found conflicting type declarations with the same name, which may indicate a build issue or a bug in Jazzy: instance method init(location:heading:name:), instance method init(location:heading:name:)

followed by a warning about each of the symbols in this library:

`Session` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
`RouteCompletionHandler` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
`MatchCompletionHandler` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
`RouteRefreshCompletionHandler` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
`shared` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
`credentials` has no USR. First make sure all modules used in your project have been imported. If all used modules are imported, please report this problem by filing an issue at https://github.com/realm/jazzy/issues along with your Xcode project. If this token is declared in an `#if` block, please ignore this message.
…

The whole docset is affected:

0% documentation coverage with 0 undocumented symbols

This issue did not affect the v2.7.0 documentation. We’ve been seeing something similar with Turf as well: mapbox/turf-swift#195.

/cc @mapbox/navigation-ios