...in X11SalGraphics::GetGlyphBoundRect

In MultiSalLayout::GetBoundRect we loop through each fallback font and union
each level's GetBoundRect to get the result, which seems reasonable, except
that for each level that means a call to SalLayout::GetBoundRect which calls
X11SalGraphics::GetGlyphBoundRect.

Those sublevel SalLayouts don't know that they are sublevels so they never set
the level bits on their glyphs. Which results in
X11SalGraphics::GetGlyphBoundRect always searching for that glyph in the level
0 font, so there's a mismatch between the font the SalLayout's are created to
use and the font that gets used.

Now, SalLayout::GetBoundRect is a fairly simple thing, it just calls
GetNextGlyphs 1 by 1 and X11SalGraphics::GetGlyphBoundRect on the result of
that.  So I *think* that if we remove the specialized
MultiSalLayout::GetBoundRect in favour of the default implementation, then
because MultiSalLayout::GetNextGlyphs is specialized to do-the-right-thing and
set up the glyph ids correctly, then we bubble the ids down
to X11SalGraphics::GetGlyphBoundRect correctly to get it to
use the right font and we get the correct bounding size.

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defb4d60a2d22fd36a0ff3f077faa6a0932b45a4

Change-Id: Idefb4d60a2d22fd36a0ff3f077faa6a0932b45a4