Adding support for more PyPy versions and installing them on-flight (#168)

* add support to install pypy

* resolved comments, update readme, add e2e tests.

* resolve throw error

* Add pypy unit tests to cover code

* add tests

* Update test-pypy.yml

* Update test-python.yml

* Update test-python.yml

* Update README.md

* fixing tests

* change order

Co-authored-by: Maxim Lobanov <v-malob@microsoft.com>

* add pypy tests and fix issue with pypy-3-nightly

Co-authored-by: Maxim Lobanov <v-malob@microsoft.com>

src/find-python.ts

@@ -1,5 +1,6 @@
 import * as os from 'os';
 import * as path from 'path';
+import {IS_WINDOWS, IS_LINUX} from './utils';
 
 import * as semver from 'semver';
 
@@ -8,9 +9,6 @@ import * as installer from './install-python';
 import * as core from '@actions/core';
 import * as tc from '@actions/tool-cache';
 
-const IS_WINDOWS = process.platform === 'win32';
-const IS_LINUX = process.platform === 'linux';
-
 // Python has "scripts" or "bin" directories where command-line tools that come with packages are installed.
 // This is where pip is, along with anything that pip installs.
 // There is a seperate directory for `pip install --user`.