Support per-window "global" values for local-to-window options

[citizenmatt]

When an option is set in Vim with :set, Vim will set the local/effective value of the option and also sets a global value. When opening a new window or editing a new buffer in the current window, Vim will (re)initialise options by copying the global value to the new window's effective options. This means last-write-wins. For non-user-visible (local-to-buffer) options such as 'fileencoding' this makes sense - the user sees the behaviour set with the last write, regardless of which window it was actually set in. For user-visible options such as 'relativenumber', this is less intuitive. The user will expect to see the same value as currently used in the current/opening window, not the last globally set value (ignoring explicitly local values set with :setlocal). In order to do this, Vim's local-to-window options maintain a per-window "global" value rather than an application wide global value (as used by local-to-buffer options).

This PR adds support for per-window "global" values for local-to-window options to IdeaVim. It can be seen in action by setting different values of the 'relativenumber' local-to-window option and using that to open new windows. IdeaVim will open the new window based on the settings in the current window, so the same look-and-feel of the opening window is maintained, similar to Vim.

This behaviour will be used by all local-to-window options, including the 'wrap' option, which will be added next - user-visible options will be correctly copied to a new window, from the opening window, providing Vim compatible, intuitive option values.

It also:

• Treats the preview tab and "reuse unmodified tabs" as opening in the same window, and initalises options correctly - as though Vim had used :edit {file}. (IntelliJ implements preview tabs and reusing tabs by simply opening a new tab and closing the previous tab). The previous PR already implemented initialising new windows from the current/opening window.
• Create a "fallback" window that is used to evaluate the ~/.ideavimrc file. This is used to capture option state and apply it to the first opened editor. Vim will initialise vimrc files in the context of the initial window and buffer, and now IdeaVim will do so too, even if there are no editors open at the time of IDE startup, or if plugin initialisation is delayed. This can be seen by the use of setlocal in ~/.ideavimrc.
• Updates the "fallback" window's option state when the last editor is closed. The next editor to open is initialised from the fallback window, and therefore maintains the per-window "global" options of the last closed window. I.e. the new editor will look like the last closed window. This mimics the behaviour of Vim, which always has at least one open window - closing the last and opening a new editor is like Vim editing a new buffer in the current ("last") window.
• Changes OptionAccessScope.GLOBAL from a singleton object to also requiring a VimEditor instance, like LOCAL and EFFECTIVE. This is necessary to be able to access per-window "global" values of local-to-window options. It is possible to pass null as this editor, but this is only valid when accessing global options and only applicable if an editor isn't available. Generally speaking, you should always pass an editor to GLOBAL.
• Minor refactorings such as renaming OptionScope to OptionAccessScope to avoid confusion with OptionDeclaredScope, and fixing some minor implementation details of adding/removing values from string and string list options.

[citizenmatt]

Just pushed an extra commit to only notify changes for options that have actually changed. This is primarily to avoid instantiating extensions when resetting the extension's option – it will instantiate the extension just to mark it inactive.

[AlexPl292]

Awesome work! Merged, thank you!