Biginset branch has landed (sorry for the spam)

[Jean-Marc Lasgouttes]

I merged the biginset branch (see #12297 for context) to master. This is 
the good part.

The bad part is that I decided first to rebase it over master, and that 
resulted in 100+ messages sent to lyx-devel :( We are investigating how 
to avoid that.

What now? Well, testing is welcome when you have time : does everything 
works the same, but faster for big document that were annoying?.

As far as 2.4 is concerned, I could (if Riki still agrees) push that to 
2.4.1-devel too. If we want to be a bit more conservative, I can push 
only the part up to "Update PAINTING_ANALYSIS" (aka the end of the list 
below), which is the most important part. I tend to think that this is a 
safer part, but actually I do not really know.

JMarc


9fd397ac1c Indicate that, by default, mouse LFUN do not require a 
metrics update
73678dcde9 Avoid full metrics computation when entering/leaving inset
5e8578837f Avoid some full metrics computations related to math previews
f7218cec18 Avoid metrics computation on resize when width did not change
1d1f95d2ed Reduce metrics updates from 4 to 1 when loading file
a23522073c Update PAINTING_ANALYSIS
2449693301 Do not compute metrics at each preview when loading file
f15d2ebf38 Improve the code that limits scrolling at top/bottom
08010c6a5e Implement quick scroll
0b6105b924 Introduce new helpers ParagraphMetrics::top/bottom
7f85024f80 In the no-draw phase, do not cache the positions of not 
visible insets
d19ade9a61 Remove some redundant calls to updatePosCache
9a96726bcd Enable Update::SinglePar in nested insets too