ArchiveHeapWriter::get_filler_size_at() cannot handle buffer expansion

Found during Leyden development as we have more objects in the CDS archive heap:

Test case with JDK mainline:

Change https://github.com/openjdk/jdk/blob/218829e0a2a3ae5599b81733df53557966392033/src/hotspot/share/cds/archiveHeapWriter.cpp#L171-L177 to

void ArchiveHeapWriter::allocate_buffer() {
  int initial_buffer_size = 1050000; // WAS 100000;
  _buffer = new GrowableArrayCHeap<u1, mtClassShared>(initial_buffer_size);
  _buffer_used = 0;
  ensure_buffer_space(1); // so that buffer_bottom() works
}

Run with

java -Xshare:dump -Xlog:cds+map*=trace:file=cds.map:none:filesize=0'

# Internal Error (/jdk3/tea/open/src/hotspot/share/cds/archiveBuilder.cpp:1075), pid=310801, tid=310811
# Error: ShouldNotReachHere()
#
# JRE version: Java(TM) SE Runtime Environment (22.0) (slowdebug build 22-internal-adhoc.iklam.tea)
# Java VM: JavaHotSpot(TM) 64-Bit Server VM (slowdebug 22-internal-adhoc.iklam.tea, interpreted mode, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x5c5781] ArchiveBuilder::CDSMapLogger::log_heap_region(ArchiveHeapInfo*)+0x1fe

===============================
Reason:

The archive heap size is about 1079504 bytes. A filler array was created just before we have allocated about 1MB objects. The address of this array is remembered in this table:

typedef ResourceHashtable<address, size_t,
      127, // prime number
      AnyObj::C_HEAP,
      mtClassShared> FillersTable;

However, as we allocate more than 1050000, the buffer is expanded, and the filler object now lives on a different address.