Wrapped long line and folding performance

[karlvr]

This is related to #159 #41.

This PR contains a few optimisation suggestions for RSyntaxTextArea, which have made an enormous difference to the performance of wrapping large single-line text files (e.g. minified JavaScript or JSON).

The first commit is a simple cache of character position in a wrapped line to line height, so we don't have to measure from the start of the string every time.

The second commit avoids measuring widths at all if we don't need to (there were places where the measurement wasn't used), and importantly, to measure only up to a maximum value if that would flip us into an alternative code path that didn't need the accurate result, e.g. in calculateBreakPosition where if the measured width is greater than the width of the text area we don't care how wide it actually was.

I think the results are still accurate!

I say this PR is a suggestion as I have simply duplicated methods in TokenImpl and the parameter names aren't A+. But if you like it @bobbylight then I'll happily tidy it up, tidy it up with you, or hand it over to you as per your preference.

Finally, thank you very much for this excellent project.

[karlvr]

There is also a rendering performance issue in WrappedSyntaxView.drawView (and the highlighted equivalent) where if we have a large View that perhaps contains thousands of tokens, we draw all of the chars in it every time we paint, rather than using the clip rectangle to limit drawing.

I have pushed a couple of commits to resolve that issue and now I'm scrolling smoothly in a view with no syntax highlighting but a huge long line.

[karlvr]

The "avoid spurious resizes" commit I think might be indicative of something wrong going on elsewhere, and is most likely the wrong fix for this issue. That will bear some more investigation

The next issue I ran into was the performance of folding on large JavaScript files, so I've added a commit to improve the performance of folding. I think I've made OK assumptions re using the same binary search approach from getFoldForLineImpl in isLineHiddenImpl... I ran the old and new algorithms in parallel on a large JavaScript file and they gave the same results... but it's always nerve-racking with off-by-one-prone code like this (e.g. the first line of a fold is visible).