Make a fallback path for drawStaticText() which uses paths for very large glyphs

Currently drawStaticText() will cache glyphs of any size. Since this does not scale at some point, and since it's not always convenient for the developer to predict or limit the sizes of the QStaticTexts, we should include a fallback to path drawing of the text. The threshold should be high enough so that QStaticText supports the relevant font sizes, but low enough that the size of the cache texture does not grow too big.