Make seec::trace::FunctionState support getCurrentRuntimeValueAs by adding the
following methods:
 - getRuntimeAddress(llvm::Function const *) const
 - getRuntimeAddress(llvm::GlobalVariable const *) const
 - getCurrentRuntimeValue(uint32_t) const
 - getCurrentRuntimeValue(llvm::Instruction const *) const

The new getCurrentRuntimeValue() methods obsolete several existing methods,
which have been removed:
 - getRuntimeValue()
 - getRuntimeValueAs<T>()

The following remains to allow direct access to RuntimeValue objects for state
modification:
 - getRuntimeValue(uint32_t Index)

Update llvm::raw_ostream printing for FunctionState objects to account for
these changes (this was the only client of the removed methods).