Icon Browser Improvements

[Meorawr]

I've activated my inner Peter and improved the icon browser in err... multiple ways.

Wow_4FRAZR1zAE.mp4

Icon grid

• We now display the selected icon first in the grid with a yellow highlight, making it easier to figure out the name of your currently selected icon if you need it elsewhere.
• Icons look a bit less ugly; they're no longer enormously oversized in the tooltip, and in the browser grid itself they now have a proper mask and set of textures for backgrounds and a pressed state.

Search

• The search box is now more standard; it displays above the grid and has the usual functionality of search boxes elsewhere in the game UI - such as a "clear" button, and placeholder text.
• The search box no longer cares about punctuation; a search for "inv axe" will return all results named like "inv_axe-33".
• The search box now debounces inputs - a new search won't be performed until 250ms have passed since the last input. This resolves flickering issues when typing into the field.
• If no search results are found, we now display an empty state with proper text instead of a blank grid.
• The result count text has been removed. With the addition of the empty state, there's not really any need for it (who cares if there's exactly 3343 icons found?).

Progress indicator

• An input blocker has been added to prevent clicking icons while a search is in progress. This is to work around API issues; ScrollBox list views seem to render their elements unclickable for a frame whenever the data provider updates, and as we're searching every game frame the icons can't be clicked anyway until the search completes. The input blocker is more intended to represent this visually by applying a dark overlay over the icons until the search is complete.
• Relocated the progress bar to sit atop the input blocker, centered over the grid. With this, it means the grid can fully expand down and display more icons than before!

Misc

• Added some sick animations and made some visual improvements to reduce flicker on Classic, which would search through icons too fast.

[Meorawr]

This is basically good to go at this point - only thing that's outstanding is whether or not I want to make the browser sort icons that are in the players' spellbook and/or equipped items first, similar to how the icon browser works in the macro window.