Remove the deferred InvalidateMeasure

[danipen]

Removed the deferred InvalidateMeasure call.

• No noticeable change in performance (tested with and without it in macOS and windows, and no perf changes).
• It obscures the API usage. Basically, when you want/need to access the VisualLines you need to use the Dispatcher too (you need to wait until at least until the control has completed a measuring cycle to ensure that the visual lines have been generated). The same thing happens for scrolling, after scrolling you need to defer any op until the visual lines have been generated. Removing it would make all usages easier since it would be always synchronous. Virtualization makes things fast enough in my opinion.