We previously waited for the initialization response from the build server during the creation of a `Workspace` so that we could create a `SemanticIndexManager` with the index store path etc. that was returned by the `build/initialize` response. This caused all functionality (including syntactic) of SourceKit-LSP to be blocked until the build server was initialized.
Change the computation of the `SemanticIndexManager` and related types to happen in the background so that we can provide functionality that doesn’t rely on the build server immediately.
Fixes#2304
When the BSP server fails to initialize, it can’t give us any compiler arguments and we won’t be able to provide semantic functionality. Show the message to the user so they can do something about fixing it instead having to dig into SourceKit-LSP logs.
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.
