Add new method to set layout-based zoom level limit

[anaisbetts]

The current behavior of setZoomLevelLimits affects the visual-based zoom (i.e. no layout changes) despite all of the rest of the methods affecting layout-based zoom. While this zoom survives in-page navigations such as iframes being loaded, it also causes pages to be cut-off.

The ideal fix for this would to be to just change the behavior of this method but that would be a breaking change. This PR introduces a new zoom level limit method to limit layout-based zoom.

This allows you to work around #6958 by doing the following:

function setZoomHarder(wv, zoomLevel) {
  wv.setLayoutZoomLevelLimits(zoomLevel, zoomLevel);
  wv.setZoomLevel(zoomLevel);
}

Refs #6958

[zeke]

Perhaps this change should be documented in

electron/docs/tutorial/planned-breaking-changes.md

Line 14 in 71f94c7

// Replace with

[kevinsawicki]

The ideal fix for this would to be to just change the behavior of this method but that would be a breaking change.

Any feels about changing the current method to accept a third type parameter so it could be something like?

wv.setZoomLevelLimits(0, 3, 'layout'); // new behavior
wv.setZoomLevelLimits(1, 2, 'visual'); // default behavior if unspecified

[anaisbetts]

@kevinsawicki Feels a little weird to me but if you think it's better I'm okay with that

[kevinsawicki]

I pushed a few changes to this branch:

• Expose and document setVisualZoomLeveLimits as public on webContents, webFrame, and <webview>
• Map setZoomLevelLimits to SetVisualZoomLevelLimits for backwards compatibility
• Add notes to planned-breaking-changes.md about setZoomLevelLimits