Add service to allow custom commands to hook in

[calebmeyer]

debug info

```json { "atom": "1.27.0", "platform": "win32", "release": "10.0.16299", "vmpVersion": "1.32.0", "vmpConfig": { "automaticallyEscapeInsertModeOnActivePaneItemChange": true, "keymapBackslashToInnerCommentOrParagraphWhenToggleLineCommentsIsPending": true, "keymapCCToChangeInnerSmartWord": true, "keymapPToPutWithAutoIndent": true, "keymapUnderscoreToReplaceWithRegister": true, "keymapYToYankToLastCharacterOfLine": true, "showHoverSearchCounter": true, "statusBarModeStringStyle": "long", "useSmartcaseForSearch": true, "useSmartcaseForSearchCurrentWord": true, "wrapLeftRightMotion": true, "blackholeRegisteredOperators": [], "startInInsertModeScopes": [], "charactersToAddSpaceOnSurround": [], "highlightSearchExcludeScopes": [], "flashOnOperateBlacklist": [] } } ```

Read and check all "Check list" bellow.

Check list

You have to check all before open issue.

• [x] Provide your environment info clipped by Vim Mode Plus: Clip Debug Info command.
• [x] Try with latest Atom and latest vim-mode-plus.
• [x] Pick descriptive and non-ambiguous subject
• [x] Express "what" you want(feature? config option?, behavior change?) in short sentence(not long!).
• [x] Contrast current behavior if you want to change current behavior, with sample text, operation(keystroke) and result.
• [x] Include real use case so that maintainer can understand "why" you need help.
• [x] Include Atom(atom --version), vim-mode-plus version, and OS version(e.g. macOS Sierra 10.12.3).
• [x] If keybinding issue, Read this.

What

I'd like for vim mode plus to provide a service that custom commands can hook into. Specifically, I'd like to be able to find out the current count from the OperationStack.

Why

I maintain the VMP macros package, and I have a request: https://github.com/calebmeyer/vim-mode-plus-macros/issues/5 to use VMPs count to replay macros more than once.

This would also allow for other packages to implement VMP commands and have them feel more native.

[t9md]

I think you can get count of current operation stack like this.

const vimState = service.getEditorState(editor)
const countOfCurrentOperationStack = vimState.operationStack.getCount()

For how to access service of vmp from your pkg, see vim-mode-plus-ex-mode as example and also read Atom's official documentation describing how service works.

[NOTE]

• vimState is core role of vmp.
• When you open text-editor, corresponding vimState is created(this is one-to-one mapping).
• A vimState have it's own operationStack instance.
• No instances are shared across vimState(text-editor) except globalState instance.