Auto merge of #20421 - talklittle:issue-20219, r=jdm

mach: android install/run: infer adb path from SDK dir

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Infer Android `adb` path from SDK directory in environment variables.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #20219 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because it is a build script change

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python/servo/command_base.py

@@ -606,6 +606,13 @@ class CommandBase(object):
     def android_aar_dir(self):
         return path.join(self.context.topdir, "target", "android_aar")
 
+    def android_adb_path(self, env):
+        if "ANDROID_SDK" in env:
+            sdk_adb = path.join(env["ANDROID_SDK"], "platform-tools", "adb")
+            if path.exists(sdk_adb):
+                return sdk_adb
+        return "adb"
+
     def handle_android_target(self, target):
         if target == "arm-linux-androideabi":
             self.config["android"]["platform"] = "android-18"