Fix text rendering with texture brushes properly in the GL2 engine

When drawing text using glyphs, the shader manager will select the "MaskFragmentShader" which requires a varying called "textureCoords" which is used to sample the glyph from the glyph texture. That's fine, except when you try to use one of the pattern brushes or a texture brush, because the src pixel fragment shader snippets for those brushes also sample from a texture (the brush texture) and use the very same "textureCoords" varying. As a quick fix for Qt 4.7.0, in these cases the engine will fall back to path rendering rather than use glyphs. However, that doesn't work for static text as there's nothing to fall back to.

This needs to be fixed properly by separating textureCoords for glyph lookups and textureCoords used for brush texture lookups.