Add modules partition.

Modules partition is a dynamic read-write partition.
- AVB is not enabled on the partition
- OTA is file-based; see follow up CL for details
- No build prop files; in particular, no build fingerprint
- No fs_config
- No notice files; notice files are included in individual APEXes

Test: build on CF
Bug: 163543381

Change-Id: Ie397b9ec61dfd1c158450d050196024604854d4d

help.sh

@@ -48,6 +48,8 @@ Common goals are:
                             Stands for "VendorDlkm, NO Dependencies"
     odnod                   Quickly rebuild the odm_dlkm image from built packages
                             Stands for "OdmDlkm, NO Dependencies"
+    mnod                    Quickly rebuild the modules image from built packages
+                            Stands for "Modules, NO Dependencies"
 
 
 So, for example, you could run: