Rename soong.environment.used with product name

From the previous work on renaming build.ninja, it was found that there
are extra dependencies from build.ninja which can be varied by
TARGET_PRODUCT : which is soong.environment.used.<tag>. This change
renames soong.environment.used to have target product between 'used' and
'<tag>' if available.

Bug: 277029044
Test: Test confirmed that build.ninja is not being re-generated
Change-Id: I987b6bd1a8b4f06dac52537e4178d8556251d254

ui/build/config.go

@@ -1124,6 +1124,9 @@ func (c *configImpl) NamedGlobFile(name string) string {
 }
 
 func (c *configImpl) UsedEnvFile(tag string) string {
+	if v, ok := c.environ.Get("TARGET_PRODUCT"); ok {
+		return shared.JoinPath(c.SoongOutDir(), usedEnvFile+"."+v+"."+tag)
+	}
 	return shared.JoinPath(c.SoongOutDir(), usedEnvFile+"."+tag)
 }