This way we can guarantee that all files passed to `UpdateIndexStoreTaskDescription` belong to the same target, which will simplify multi-file indexing.
The term *build system* predated our wide-spread adoption of BSP for communicating between SourceKit-LSP to the build system and was never really the correct term anyway – ie. a `JSONCompilationDatabaseBuildSystem` never really sounded right. We now have a correct term for the communication layer between SourceKit-LSP: A build server. Rename most occurrences of *build system* to *build server* to reflect this. There are unfortunately a couple lingering instances of *build system* that we can’t change, most notably: `fallbackBuildSystem` in the config file, the `workspace/waitForBuildSystemUpdates` BSP extension request and the `synchronize-for-build-system-updates` experimental feature.
If a source file is part of multiple targets, we should index it in the context of all of those targets because the different targets may produce different USRs since they might use different build settings to interpret the file.
