This was OString already; use it that way

Change-Id: Ia2268ce8a1e2111adb609c515e5bfa824afa66ce
FastSerializer: Simplify cache to be fixed sized buffer

This makes writeBytes(), which is called a lot, simpler and thus faster.
E.g. for ~15m calls, this saves ~110m pcycles.

Change-Id: I29d01a1a8651f668aff574e0f015cd2f018eb1cd
Use OUStringBuffers for performance reasons.

Saves 120m pcycles in just 250k calls to ScAddress::Format.

Change-Id: Ibf20cf0843a47cf0fa37a38c4fecf1ae1560412c
FastSerializer: Use faster TokenValue struct when possible

Saves another ~100m pcycles for 650k calls in startElementInternal()

Change-Id: I190326edc7feffb900e91fa7e5c3530b5b267f59
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
FastSerializer: Faster write(OUString): add ascii check

Saves about 80m pcycles for 180k calls.

Change-Id: I9c9b3bf5a076df56d1b5b87f0a85ac3404abe8a4
maTokenNames.size() is constant: use it and be a bit faster

Change-Id: I39a6e2badf0c159e87763e2782bc89f0ee6068ec
Remove few pointless OUString::number() and one method

Change-Id: I3e9a302a7513eebfeff07402f71fc3dde22e4cc2
FastSerializer: Use -1 for unknown string length

Change-Id: I3920caf9d95f20992b7961873f1668468d797e8e