4435.feat

The Dafny IDE now has improved behavior when working with a Dafny file that's part of a Dafny project. A Dafny file is part of a project if a `dfyconfig.toml` can be found somewhere in the file's path hierarchy, such as in the same folder or in the parent folder. A `dfyconfig.toml` can specify which Dafny options to use for that project, and can specify which Dafny files are part of the project. By default, the project will include all .dfy files reachable from the folder in which the `dfyconfig.toml` resides. Project related features of the IDE are:
- Whenever one file in the project is opened, diagnostics for all files in the Dafny project are shown. When including a file with errors that's part of the same project, the message "the included file contains errors" is no longer shown. Instead, the included file's errors are shown directly.
- If any file in the project is changed, diagnostics for all files in the project are updated. Without a project, changing an included file will not update diagnostics for the including file until the including file is also changed.
- The find references feature (also added in this release), works better in files that are part of a project, since only then can it find references that are inside files that include the current file.
- The assisted rename feature (also added in this release), only works for files that are part of a project.
- When using a project file, it is no longer necessary to use include directives. In the previous version of Dafny, it was already the case that the Dafny CLI, when passed a Dafny project file, does not require include directives to process the Dafny program. The same now holds for the Dafny IDE when working with Dafny files for which a project file can be found.
- If any file in the project is resolved, all files in the project are resolved. Opening a file in a project that's already resolved means the opened file is resolved instantly.
- The IDE's memory consumption stays the same regardless of how many files in a project are opened. Without a project, the IDE increases it's memory usage for each open file.

Try out the IDE's project support now by creating an empty `dfyconfig.toml` file in the root of your project repository.