WIP: Implementation of file system abstraction.
Fully implement package map.

Note: At this point, it seems the analysis server is actually processing all files of a test project, without any exception thrown. Next step is to trying to retrieve build errors.
Split into separate files.
Renames.
Working implementation of "get analysis error" end-2-end.

Note: this currently only work for the initial call to "processChanges". We do not support yet incremental changes.
Fix issue where import to local files are not resolved properly.
Comments.
Fix FileUriResolver implementation to take into account new URI format of source files.

We use to encode only the relative path for application file URI. The path now includes the project root path, as it is needed for the analysis_server virtual file system. This broke the implementation based on the analyzer only. This CL fixes that issue.
Minor code cleanup.
WIP: Remove "RunInZone" to allow for debugging in Dart Editor.
Minor rename.
Log errors from analysis server.
Log calls to "getFolderChanges"
Log package map creation results.
Extract RequestIdFactory interface.

* Request ID need to be unique per analysis server instance, not per project context.