Scala-native: Implement conversions between numeric primitives and `java.lang.String`

[densh]

Due to incomplete java.lang.String support in the past we could not properly implement toString and parse methods for numeric types: java.lang.{Byte, Short, Int, Long, Float, Double}. Those can be easily ported over from Apache Harmony, especially considering that we use similar implementation of strings.

• [x] java.lang.Byte
• [x] java.lang.Short
• [x] java.lang.Integer
• [x] java.lang.Long
• [x] java.lang.Float
• [x] java.lang.Double

[densh]

@t-hiroyoshi Would you be interested in having a look at this one? Should be quite related to your previous work on java.lang.String.

[t-hiroyoshi]

@densh OKay, I'll do this!

[densh]

@t-hiroyoshi Cool, thanks!

[densh]

@t-hiroyoshi It looks like you're mostly done with support for integer types. Can you open pr for that part?

[densh]

First half of the work has been merged in https://github.com/scala-native/scala-native/pull/238. We're only missing floating point types now.

[densh]

I've moved out unsigned string conversions into separate issue https://github.com/scala-native/scala-native/issues/242 as those are not as critical.

[densh]

Fixed in https://github.com/scala-native/scala-native/pull/262