Move FormulaToken::TextEqual overrides down into specific subclasses

Change-Id: I5f27054ef2f9fdc4d0be0afe91ad31d053976bcf
Turn static ScToken::ExtendRangeReference into free function

...and rename to extendRangeReference to avoid confusion with
formula::FormulaCompiler::ExtendRangeReference.

Change-Id: Ifcad309c14e04a0e37c80ca44462da587387241d
loplugin:saloverride

Change-Id: I94f330d31f142bbeea2274597c855481cb311e0c
Turn virtual ScToken::Dump into a single free function DumpToken

Change-Id: I2c81f24a27ede9922ed8ff16cf0ea4af824e9e59
Make ScToken::GetSingleRef etc. return * instead of &

...so that default implementations can return nullptr without further ado

Change-Id: Idc8778fe868efa00b1de597a54aa07a2e6fa3bc0
Move virtual ScToken members up to FormulaToken

Change-Id: I20eb3b44d540f459cd1902a7a3b6a5c867e5bc07
Turn ScToken::checkTextEqual into a free function

Change-Id: I03daf7bb68ed33d9610b7ef19d3bd6c18dc8170f
Remove ScToken from the formula::FormulaToken hierarchy

...to keep UBSan from complaining about illegal downcasts from FormulaToken to
ScToken (which were practically harmless, given that ScToken did not add any
data members).

Change-Id: I8fdc026eec363442cc4b720b71d65c972b4a4446