A lot of those features were in visual studio 6, which was released in the late 90s or early 00s. Tabbed files, syntax highlighting for their supported formats (though it was a lot more tightly bound to those languages, like there was a visual basic program and a separate visual c/c++, n++ is the first I remember with arbitrary language syntax highlighting support), pretty sure it had a plugin system, too.
And vs6 was just the first one I used, they might have been present in vs5 or earlier versions.