[ENG-15045] add `--linker` and copyfile fallback for isolated installs

Merged
DY
1y ago
+613-121

What does this PR do?

  • Packages will be installed by copying files when hardlink or clonefile received XDEV
  • Added --linker=isolated and --linker=hoisted
  • fixes progress bar for isolated installs
  • fixes counting installed packages for the install summary

How did you verify your code works?

Added tests for install backends and --linker