Closes #1165 - Adds options to modify file annotation button behaviour

[arrpee]

Description

Adds two options to modify the behaviour of the file annotations button:

• "gitlens.menus.annotations.behaviour" changes the behaviour between a menu (default) and a toggle button
• "gitlens.menus.annotations.toggleType" changes what is toggled when behaviour is set to toggle

I wasn't too sure of what to name the settings so if you can suggest more appropriate ones that would be great.

Checklist

• I have followed the guidelines in the Contributing document
• My changes follow the coding style of this project
• My changes build without any errors or warnings
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[eamodio]

Thanks for the contribution!

Unfortunately we can't use the gitlens.menus setting as you have here, since it will break how that setting is used elsewhere (since its set as an object). So we'll need to come up with another setting name -- maybe add a new fileAnnotations.command setting, that defaults to null (which would mean show the menu), or be an enum of blame, changes, heatmap. We probably will also need to add a fileAnnotations.diffCommand setting, which is the same as fileAnnotations.command, but can't be set to changes.

[arrpee]

I've combined and replaced the settings with fileAnnotations.command. What would fileAnnotations.diffCommand be used for?

[eamodio]

@arrpee Thanks! Looking great!

I currently have the Changes file annotations disabled when you are in a diff editor -- but thinking about that more I don't think that is needed anymore. So I think we can just move ahead without anything like fileAnnotations.diffCommand

[eamodio]

Just need to remove this and document the new gitlens.fileAnnotations.command

[arrpee]

I've made the changes

[eamodio]

Thank you so much for your contribution!