Add a script to inject values into manifests

Add a script that can inject a <uses-sdk minSdkVersion=""> into
AndroidManifest.xml files.  This will help with merging
LOCAL_STATIC_ANDROID_LIBRARIES, because ManifestMerger treats
a missing minSdkVersion as minSdkVersion=1 and throws errors
if libraries use a larger minSdkVersion.  It will also help
with cases where an app has a manifest that specifies an old
minSdkVersion, but the build system is compiling the app in
a way that is not compatibile with old devices, for example
using a newer dex format.

Bug: 110167203
Test: m java
Test: build/soong/scripts/manifest_fixer_test.py
Change-Id: I528d71a225feb86464c530e11b223babb0ea9edf

java/config/config.go

@@ -132,4 +132,6 @@ func init() {
 	}
 
 	hostBinToolVariableWithPrebuilt("Aapt2Cmd", "prebuilts/sdk/tools", "aapt2")
+
+	pctx.SourcePathVariable("ManifestFixerCmd", "build/soong/scripts/manifest_fixer.py")
 }