Better way to detect tools' path

[fannheyward]

Couldn't the logic be something like this? If pythonPath has been resolved to something in a virtualenv (e.g. .venv/bin/python). Store const venvBinPath = path.dirname(pythonPath). And then when running mypy you first try path.join(venvBinPath, 'mypy'). And if that fails, look in $PATH?

You could maybe even do that logic during startup and save the absolute path to the binary so you don't have to run a subprocess twice in the global case.

Originally posted by @lithammer in #917 (comment)

[fannheyward]

Currently steps:

1. get tool's path from setting, execPath = mypy
2. use which to get full exec path
   • execPath = /full/path/to/global/mypy
   • or execPath = /path/to/project/.venv/bin/mypy
3. now basename never equal to execPath, module name is undefined
4. run in sub process mode, /full/path/to/mypy xxx

This detection can use global and local tools, but breaks module mode.

[fannheyward]

Another issue #901, rope can only be run in module mode, the detected Python bin must install rope to use.