Use sc::CompileFormulaContext for faster export

It's a cache for maTabNames (sheet names mangled for the current grammar
for output) which ScCompiler needs and is expensive to get.

Change-Id: I7e2954104427a3c220f0f097be6cd45a66485b56
Unused includes / using-declarations

Change-Id: I8b43635ab1f77b61469f060c9a092f1494388955
FastSerializer: Simplify a bit

Change-Id: I7dee908f5441ad34128d688e1008fd6ffad2ab3f