integer conversions:
- improve `u32toa_radix` and `u64toa_radix`, add `i32toa_radix`
- use `i32toa_radix` for small ints in `js_number_toString`
floating point conversions (`js_dtoa`):
- complete rewrite with fewer calls to `snprintf`
- remove `JS_DTOA_FORMAT`, define 4 possible modes for `js_dtoa`
- remove the radix argument in `js_dtoa`
- merge `js_dtoa1` into `js_dtoa`
- add `js_dtoa_infinite` for non finite values
- simplify sign handling
- handle locale specific decimal point transparently
helper function `js_fcvt`:
- simplify `js_fcvt`, remove `js_fcvt1`, reduce overhead
- round up manually instead of using `fesetround(FE_UPWARD)`.
helper function `js_ecvt`:
- document `js_ecvt` and `js_ecvt1` behavior
- avoid redundant `js_ecvt1` calls in `js_ecvt`
- fixed buffer contents, no buffer copies
- simplify decimal point handling
- round up manually instead of using `fesetround(FE_UPWARD)`.
miscellaneous:
- remove `CONFIG_PRINTF_RNDN`. This fixes some of the conversion errors
on Windows. Updated the tests accordingly
- this fixes a v8.sh bug on macOS: `0.5.toFixed(0)` used to produce `0` instead of `1`
- add regression tests, update test_conv unit tests
- add benchmarks for `toFixed`, `toPrecision` and `toExponential` number methods
- benchmarks show all conversions are now 40 to 45% faster (M2)
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