Refactor the feature to collapse unchanged sections

[kingcean]

67 Ignore unchanged lines is a notable feature to enable a way to collapse some of lines unchanged. I appreciate the contributor/author to provide such great idea and cost time to implement it.

In this PR, I have rewritten those codes by a different new way to boost performance and to apply it to all controls.

Performance enhancement

Speed up to 3-6x (test locally) in following scenarios.

• Toggle between the mode of if need to collapse unchanged sections.
• Modify the count of the context line. Context lines are the ones unchanged around others but keep visible to let end-users have a way to get context.

Controls

The old implementation was only for DiffViewer control but now (in this PR) this feature also supports SideBySideDiffViewer control and InlineDiffViewer control.

Plus, for context menu of header in DiffViewer control, I have also added the menu items to get and set the count of the context line directly when the unchanged sections are collapsed.

Other updates

Fix following bugs brought in by old implementation to ignore unchanged lines. It re-organizes the input data but neglects some corner-cases. These codes have been removed/reverted here during I rewrite all the logic.

• In particular cases, the last line of old text may miss if that line is not empty but the new one is.
• Fails to run if the old text is empty. Sounds #70 also want to fix this issue but no need now.

And improve following items.

• Robustness optimization to avoid the exception thrown mentioned in #55.
• Optimize for identical texts.

[mmanela]

@kingcean Thanks for the change. I am testing it and I dont see the new context menu.

[kingcean]

Hi @mmanela, please right click Old or New at the top of the window to popup that context menu and you will see Unified View, Split View and Collapse unchanged sections menu items there. After select Collapse unchanged sections, a new menu item Lines for context appears in that menu context (you need right click again to see).

And you can also left click (or tap) the ellipse (…) button in next to the button Switch mode at bottom to pop-up that context menu.