hgview #109862 Allow intuitive display of "heavy file" in the diff panel [done]

A button **directly** in the diff panel instead of the help text would fit.

Removing the global state from the toolbar by default in the process. I will remain in the contextual menu for people who need it.

prioritynormal
typebug
done in<not specified>
load1.000
load left0.000
closed by<not specified>
patch[qt4] add an intuitive link to display heavy files [reviewed][qt4] hide text area on heavy file [reviewed][qt4] hide text area on heavy file [applied][qt4] add an intuitive link to display heavy files [applied][qt4] add an intuitive link to display heavy files (closes #109862) [rejected][qt4] add an intuitive link to display heavy files (closes #109862) [rejected][qt4] hide text area on heavy file [rejected][qt4] add an intuitive link to display heavy files (closes #109862) [rejected][qt4] add an intuitive link to display heavy files (closes #109862) [rejected]