Bug 1844838 - Use default python3 outside MozillaBuild on Windows r=m_kato,geckoview-reviewers

The current method fails when Mach is called outside MozillaBuild (https://firefox-source-docs.mozilla.org/mach/windows-usage-outside-mozillabuild.html), as `./mach environment` called inside gradle uses different Python and causes conflict in `~/.mozbuild`.

Differential Revision: https://phabricator.services.mozilla.com/D184255

mobile/android/mach_commands.py

@@ -5,6 +5,7 @@
 import argparse
 import logging
 import os
+import sys
 
 import mozpack.path as mozpath
 from mach.decorators import Command, CommandArgument, SubCommand
@@ -492,6 +493,8 @@ def gradle(command_context, args, verbose=False):
             "GRADLE_OPTS": "-Dfile.encoding=utf-8",
             "JAVA_HOME": java_home,
             "JAVA_TOOL_OPTIONS": "-Dfile.encoding=utf-8",
+            # Let Gradle get the right Python path on Windows
+            "GRADLE_MACH_PYTHON": sys.executable,
         }
     )
     # Set ANDROID_SDK_ROOT if --with-android-sdk was set.

settings.gradle

@@ -5,15 +5,8 @@ def topsrcdir = rootProject.projectDir.absolutePath
 apply from: "${topsrcdir}/mobile/android/gradle/mach_env.gradle"
 
 def commandLine = ["${topsrcdir}/mach", "environment", "--format", "json", "--verbose"]
-if (System.properties['os.name'].toLowerCase().contains('windows')) {
-    // gradle is called before parsing config.status, we cannot use PYTHON
-    // value.
-    if (System.env.MOZILLABUILD) {
-        def mozillabuild = System.env.MOZILLABUILD.toLowerCase()
-        if (mozillabuild) {
-            commandLine.addAll(0, ["${mozillabuild}/python3/python3.exe"])
-        }
-    }
+if (System.env.GRADLE_MACH_PYTHON) {
+    commandLine.addAll(0, [System.env.GRADLE_MACH_PYTHON])
 }
 
 def proc = commandLine.execute(machEnv(topsrcdir), new File(topsrcdir))