Add ToIntegerBase for explicit integer parsing

[sagikazarmark]

Summary

• add an exported Integer constraint for signed and unsigned integer conversions
• add ToIntegerBase and ToIntegerBaseE for explicit base-aware integer parsing
• keep ToNumber focused on generic numeric casting without exposing a base-aware float API

Related

• Casting a string to int with a 0 in prefix does not work as expected #74
• bug of toInt toInt32 toInt64 #96
• toInt/toInt64 is wrong #112
• the function ToInt sometimes has some mistakes #133
• cast.ToInt("08") returned 0 #147
• cast.ToInt64E("16025123132364928") return 0 #162
• Unexpected results with padded strings #182
• cast toint32 but return zero #202
• cast.ToInt("08") return 0 and so on #214
• ToInt have bad case #216
• why cast.ToInt("08") return 0 then cast.ToInt("07") return 7 ?  #220
• fix:string to uint64 error #228
• cast.ToUint32("0134444") = 47396 #232
• toIntBase10 enforces base 10 conversion #91
• add func Atoi to convert string base 10 #152
• Unexpected number conversion #258
• the code「cast.ToInt("08") 」 has unexpected value result #290