Move manifest_fixer to a python_binary_host module

In preparation for making it use multiple files so that some
implementation can be shared with a new tool.

Also make manifest_fixer_test a python_test_host, and add it
to TEST_MAPPING.

Test: m checkbuild
Change-Id: Iaae177efcb978187b126d90359b82cdfd3176857
diff --git a/java/config/config.go b/java/config/config.go
index 46cd361..adf9c92 100644
--- a/java/config/config.go
+++ b/java/config/config.go
@@ -142,7 +142,7 @@
 
 	hostBinToolVariableWithPrebuilt("Aapt2Cmd", "prebuilts/sdk/tools", "aapt2")
 
-	pctx.SourcePathVariable("ManifestFixerCmd", "build/soong/scripts/manifest_fixer.py")
+	pctx.HostBinToolVariable("ManifestFixerCmd", "manifest_fixer")
 
 	pctx.HostBinToolVariable("ManifestMergerCmd", "manifest-merger")