This isn't really an extension, but I use it very often.
I was looking for something equivalent to Sublime's panel focus, and there's a key map option, but it's not set to any key by default:
View: Maximize Editor Group and Hide Side Bar (shift + alt + enter)
View: Reset Editor Group Sizes (ctrl + shift + alt + enter)
View: Maximize Editor Group and Hide Side Bar
View: Reset Editor Group Sizes
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