OMS: include idmap data in dump

Teach the overlay manager to ask the idmap service to pretty print the
contents of each idmap file as part of OMS dump. This creates a single
entry point for dumping both OMS and idmap data, and circumvents the
problem of accessing the idmap service if it has been killed due to
inactivity.

Example idmap section:

---- 8< ----
IDMAP OF com.android.theme.color.sand
Paths:
    target path  : /system/framework/framework-res.apk
    overlay path : /product/overlay/AccentColorSand/AccentColorSandOverlay.apk
Debug info:
    W failed to find resource 'string/accent_color_overlay'
Mapping:
    0x0106006e -> 0x7f010000 (color/accent_device_default_dark -> color/accent_device_default_dark)
    0x01060070 -> 0x7f010001 (color/accent_device_default_light -> color/accent_device_default_light)
---- >8 ----

Bug: 189963636
Test: adb exec-out dumpsys
Test: adb exec-out cmd overlay dump
Test: adb exec-out cmd overlay dump <overlay-identifier>
Change-Id: I9de6ba646ad4714c9d0f0d8081fbf632577107e7