Split ISyntaxFactsService into two parts:

1. `ISyntaxFacts`: Pure data interface to query about syntactic facts. This is moved to CompilerExtensions shared project and can be used by analyzers.

2. `ISyntaxFactsService`: Derives from ISyntaxFacts and ILanguageService and is present in the WorkspaceExtensions shared project. This enables Code fixes and Workspaces layer to access the same functionality via a language service, i.e. `GetLanguageService<ISyntaxFactsService>`.

Note that we cannot use a partial declaration for `ISyntaxFactsService` instead of `ISyntaxFacts`. This causes `ISyntaxFacts` to be defined in both the CodeStyle analyzer and CodeStyle fixer assembly (former imports CompilerExtensions and latter imports WorkspaceExtensions), which leads to type conflicts. We also cannot follow the approach taken for `ISyntaxKindsSevice` as it defines the second partial declaration `ISyntaxKindsSevice` which sub-types `ILanguageService` in Workspaces project, leading to the language service not being defined in CodeStyle fixer assembly, which will cause any code fix requesting `GetLanguageService<ISyntaxKindsService>` to fail. The only feasible approach for us to have the functionality available in shared analyzer layer is to split out the pure data query part of the service to a separate type, as done in this PR. I will send a follow-up PR to also split `ISyntaxKindsService` similarly. Hoepfully, these two are the only language services that are commonly used by our analyzers, and we will not require any more such splits.