Add units tests to check that the Floating Point registers are being properly saved

[RichieSams]

Previous versions of the asm files ignored the FP registers. So a fiber switch could corrupt the data left in the registers.

We should create a set of unit tests to check that this does not happen. I'm thinking something similar to the current SingleFiberSwitch and NestedFiberSwitch, but using floating point numbers instead of integers.

The hard part will be dealing with floating point rounding errors.

[RichieSams]

After testing a bit with Godbolt, the floating point tests I added don't accomplish anything. Everything is saved through the stack.

To get a real test of all the registers, we will need to create asm functions that do the following:

1. Fill all the registers
2. Call jump_fcontext
3. In the new context, modify the registers
4. Jump back to the first context
5. Test the contents of the registers to see that they are preserved