androidfw: Add support for 16-bit entry offsets

Bug: 237583012

Most offsets to the entries can be well encoded in 16-bit,
and given entries are 4-byte aligned, this gives us a range
of entry offsets from 0x00000 to 0xfffe * 4u, with 0xffffu
to represent ResTable_type::NO_ENTRY.

For now, 16-bit entry offset will be enabled only when:

 * all the entry offsets can be represented in 16-bit
 * --enable-compact-entries switch is turned on

Change-Id: I1c815c052aa5fba6eab2529434d31d7714c13694