sys.executable reports path to R on Windows

[kevinushey]

For example, I see on Windows in RStudio:

> sys <- import("sys")
> sys$executable
[1] "C:\\Program Files\\RStudio\\resources\\app\\bin\\rsession-utf8.exe"

Similarly, in RGui:

> sys <- import("sys")
> sys$executable
[1] "C:\\R\\R-4.2.1\\bin\\x64\\Rgui.exe"

We might want to fix this up to point at the path to the "real" Python executable associated with the Python instance we have bound to.