Rollup merge of #42343 - cuviper:install-executables, r=alexcrichton

Update rust-installer for Windows executable mode

It now marks a few whitelisted extensions as executable in the tarball,
so Windows packages can be extracted on other platforms and directly
execute install.sh.

It also includes a fix for the chmod on bulk dirs, so now the html docs
won't be marked executable en masse.

Fixes #42121
r? @alexcrichton

Author: Mark-Simulacrum