[analyzer] Fix assertion failure in SMT conversion for unary operator on floats

In the handling of the Symbols from the RangExpr, the code assumed that
the operands of the unary operators need to have integral type.
However, the CSA can create SymExpr with a floating point operand, when
the integer value is cast into it, like `(float)h == (float)l` where
both of `h` and `l` are integers.

This patch handles such situations, by using `fromFloatUnOp()` instead
of `fromUnOp()`, when the operand have a floating point type.

I have investigated all other calls of `fromUnOp()`, and for one in:

 - `getZeroExpr()` is applied only on boolean types, so it correct
 - `fromBinOp()` is not invoked for floating points
 - `fromFloatUnOp()` I am uncertain about this case and I was not able
   to produce a test that would reach this point, as a negation of
   floating points numbers seem to produce `Unknown` symbols.

This issue exists since the introduction of `UnarySymExpr` in D125318
and their handling for Z3 in D125547.

Patch by Tomasz Kamiński.

Reviewed By: mikhail.ramalho

Differential Revision: https://reviews.llvm.org/D140891