Reland: Move the Once cache for dexpreopt.GlobalConfig into the

dexpreopt package.

Preparation for a future CL that will need to get the make-written
GlobalConfig from within dexpreopt.

Also rename the Load*Config functions to Parse*Config, since they don't
actually load the config files anymore.

This relands https://r.android.com/1211982.

Bug: 145934348
Test: m
Change-Id: Icb9332a93811d77d2d8b06e983b92501b180a358

java/dexpreopt_bootjars_test.go

@@ -49,7 +49,7 @@ func TestDexpreoptBootJars(t *testing.T) {
 	pathCtx := android.PathContextForTesting(config)
 	dexpreoptConfig := dexpreopt.GlobalConfigForTests(pathCtx)
 	dexpreoptConfig.BootJars = []string{"foo", "bar", "baz"}
-	setDexpreoptTestGlobalConfig(config, dexpreoptConfig)
+	dexpreopt.SetTestGlobalConfig(config, dexpreoptConfig)
 
 	ctx := testContext()