Investigate use of Editor Snapshots to improve performance

[mrlacey]

Look to improve performance when updating the UI through the use of snapshots. See https://docs.microsoft.com/en-us/visualstudio/extensibility/inside-the-editor?view=vs-2017#a-closer-look-at-the-text-model-and-the-text-view

Also various entries in https://github.com/Microsoft/VSSDK-Extensibility-Samples/