idmap2: add debug information to idmap file format

Add a new variable length string to the idmap file format. This string will
hold debug information like fulfilled policies and any warnings triggered while
generating the file.

Bump the idmap version to 3.

Adjust the idmap header definition in ResourceType.h to take the new string
into account.

Example debug info:

  $ idmap2 create \
        --target-apk-path frameworks/base/cmds/idmap2/tests/data/target/target.apk \
        --overlay-apk-path frameworks/base/cmds/idmap2/tests/data/overlay/overlay.apk \
        --idmap-path /tmp/a.idmap \
        --policy public \
        --policy oem

  $ idmap2 dump --idmap-path /tmp/a.idmap
  target apk path  : frameworks/base/cmds/idmap2/tests/data/target/target.apk
  overlay apk path : frameworks/base/cmds/idmap2/tests/data/overlay/overlay.apk
  I fulfilled_policies=oem|public enforce_overlayable=true
  W failed to find resource "integer/not_in_target" in target resources
  0x7f010000 -> 0x7f010000 integer/int1
  0x7f02000c -> 0x7f020000 string/str1
  [...]

  $ idmap2 dump --idmap-path /tmp/a.idmap --verbose
  00000000: 504d4449  magic
  00000004: 00000003  version
  00000008: 76a20829  target crc
  0000000c: c054fb26  overlay crc
  00000010: ........  target path: frameworks/base/cmds/idmap2/tests/data/target/target.apk
  00000110: ........  overlay path: frameworks/base/cmds/idmap2/tests/data/overlay/overlay.apk
  00000210: ........  debug info: ...
  00000294:       7f  target package id
  00000295:       7f  overlay package id
  [...]

Also, tell cpplint to accept non-const references as function parameters:
they make more sense as out-parameters than pointers that are assumed to
be non-null.

Also, switch to regular expressions in the RawPrintVisitorTests: no more
manual fixups of the stream offsets! Tell cpplint that the <regex>
header is OK to use.

Bug: 140790707
Test: idmap2_tests
Change-Id: Ib94684a3b4001240321801e21af8e132fbcf6609