Remove async loading from merge request's File Tree

What does this MR do and why?

This MR removes:

1. File Tree worker which is adding unnecessary overhead to the file tree data processing. Processing this data on the main thread does not introduce a significant thread blocking (the whole task takes less than 30 μs, ).
2. Virtual scrolling components async loading. Loading these components asynchronously increases bundle size and loading times because of waterfall effect (we have to load the app before we start fetching these components).

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