This PR fixes #97165

The issue here was that while DiffEditorInput is an instance of SideBySideEditorInput, it still allows for inline editing based on the config value diffEditor.renderSideBySide.

My proposed fix involves handling that case and centering appropriately, as well as calling Layout.centerEditorLayout when the configuration changes since centering behaviour is now contingent on the above configuration option.

One thing to note is that this will also cause the layout to be centered/uncentered when workbench.editor.centeredLayoutAutoResize changes, since we're also using this config option to determine centering behaviour. I think the fact that we weren't already updating based on config changes counts as a bug as well.

To test these changes use the test case outlined in the issue(#97165)