Add fast path for margin decoration access

[joyceerhl]

For #179725

[alexdima]

👏 Very nice!

I pushed a change where I remove both the onlyMinimapDecorations and onlyGlyphMargin flags from the caching logic in viewModelDecorations because the initial idea was that there are all these view parts that need to fetch the decorations that are in the viewport and all of these callers would benefit from this single cache, and the cache would be busted only once per frame.

But already with the addition of onlyMinimapDecorations from a few months ago (d53f4c5), this initial idea was no longer working properly, as the call from minimap.ts ended up breaking the cache due to the larger range (not just the viewport) the minimap uses.

So I made a special getter for the minimap call and I also left that the glyph margin view part ends up fetching all the decorations in the viewport and does filtering based on options.glyphMarginClassName in its implementation, as this allows it to get a cache hit for the viewport, just like everyone else.