Non-ascii arguments in the native encoding are garbled on Windows

[gaborcsardi]

Because processx assumes that they are in UTF-8. R 4.0.2, Windows 10:

ASCII app:

local_temp_dir()
name <- enc2native("\u00fa\u00e1\u00f6")

out <- run(get_tool("px"), c("writefile", "of", name))
expect_equal(
    charToRaw(name),
    readBin("of", what = "raw", n = 100)
)
#> Error: charToRaw(name) not equal to readBin("of", what = "raw", n = 100).
#> 3 element mismatches

Unicode app:

out2 <- run(get_tool("pxu"), c("writefile", "of2", name))
expect_equal(
    iconv(name, to = "UCS-2LE", toRaw = TRUE)[[1]],
    readBin("of2", what = "raw", n = 100)
)
#> Error: iconv(name, to = "UCS-2LE", toRaw = TRUE)[[1]] not equal to readBin("of2", what = "raw", n = 100).
#> 6 element mismatches

[gaborcsardi]

Closed by #265.