bin/nvh: Add --force-use-xz command-line flag

Activates "force use xz" state, which skips xz-related sanity checks.

bin/nvh

@@ -309,6 +309,7 @@ Options:
   --insecure          Turn off certificate checking for https requests (may be needed from behind a proxy server)
   -p, --preserve      Preserve npm and npx during install of node
   --use-xz            Download xz-compressed tarballs, if available and extractable by tar, during install of node (this is the default)
+  --force-use-xz      Download xz-compressed tarballs. May fail if xz tarball is not available and extractable
   --no-use-xz         Download gzip-compressed tarballs, rather than xz-compressed ones, during install of node
   -V, --version       Output version of nvh
 
@@ -1200,6 +1201,7 @@ function main() {
       -p|--preserve) NVH_PRESERVE_NPM="true" ;;
       --no-preserve) NVH_PRESERVE_NPM="" ;;
       --use-xz) NVH_USE_XZ="true"; g_xz_force_enabled="false" ;;
+      --force-use-xz) NVH_USE_XZ="true"; g_xz_force_enabled="true" ;;
       --no-use-xz) NVH_USE_XZ="false" ;;
       -V|--version) echo "${VERSION}"; exit ;;
       -*) abort "unrecognised option '$1'"; exit 1 ;;