Merge: abstract_compiler: Replace the use of `n_float` by the `value`

## Added methods
Add a little improvement of the abstract_compiler to generate a Float value by the usage of the `value` and not the `n_float`.

Add the float conversion in exponential hexadecimal notation.

```
	assert 12.345.to_hexa_exponential_notation    == "0x1.8b0a3d70a3d71p+3"
	assert 12.345.to_hexa_exponential_notation.to_f == 12.345
```

## Future work

Take into account the scientific notation for the display.

Pull-Request: #2778
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>