Support hex floating point format in fmt.parseFloat and fmt.print

[tiehuis]

We should support hexadecimal floating point values in fmt.format and fmt.parseFloat.

For example, the following should hold true.

std.testing.expectEqual(std.fmt.parseFloat(""0x1.999999999999ap-4"), 0.1);

For print as a hexidecimal, a "{x}" format specifier seems most appropriate. Related to #1358 but can be done independently.

[shawnl]

Ahh, the compiler cheats by using strtod()

[corona10]

@tiehuis @shawnl

Hi devs, Is there any progress? Or can I take a look at this issue if no one works on it?

[tiehuis]

No progress on my end, and I am not aware of anyone working this. I think it'll be fine for you to work on this.

[corona10]

@tiehuis
Great! I will take a look!

[daurnimator]

@corona10 did you get anywhere with this?

[corona10]

@daurnimator Currently not, I will ping you if I am not able to work on this issue. Thanks!

[corona10]

@daurnimator If you have any progress with this issue, please handle this issue. For me, this issue might need times.

[arBmind]

Both fmt.format and fmt.parseFloat already support hex floats.

@daurnimator This issue can be closed I guess.