Minor additions to FlafLaf customs

[iajn]

I have these two properties in my NetBeans IDE FlatLaf config:

# Unify heap view chart color with accent
nb.heapview.chart = @accentColor
# Unify drop target highlight with accent
Panel.dropTargetGlassPane = @accentColor

The final colors could use some adjusting (for example the active tab indicator color seems to be a little bit darker than the accent color, unless I'm imagining things), but adding these would make the IDE look just a little bit nicer.

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Side note: the TopComponent drag and drop highlight is a little bit off from the bottom, looks like its not accounting for the tab size or something. Multirow tabs has this setup correctly for editor tabs, but those look slightly off otherwise (missing border, weird tab highlight). Not sure if these kind of things are worth reporting though, cause they are rather cosmetic?