oom on msapps with large files

[MikeStall]

The basic problem is that we load the entire msapp into memory (CanvasDocument).

And then oom at places like this:

                        case FileKind.AppCheckerResult:
                            var appChecker = Encoding.UTF8.GetString(entry.ToBytes());
                            app._entropy.AppCheckerResult = appChecker;
                            break;

We should calculating this in a streaming way rather than ToBytes(). (sarif file can be huge)

We should scrutinize usage of FileEntry.ToBytes, and probably need to be lazier and have documents backed by disk.

[MikeStall]

This is a broader problem ... we load all files into memory for CanvasDocument. Sarif is one example (and we load that into entropy), but we track all the other files too:

internal Dictionary<string, FileEntry> _unknownFiles = new Dictionary<string, FileEntry>();

internal Dictionary<string, FileEntry> _assetFiles = new Dictionary<string, FileEntry>(StringComparer.Ordinal);

For example, we might hit this problem with large resource or asset files. Screens and connections are smaller and probably not an issue.