[tools] Commit memory debug (et al) tooling

These are some changes I made to debug tooling while tracking down the
bugfix in the previous commit.

Each `scripts/debug_*_alloc.gdb` script has gdb output a `*_allocs.txt`
file, which in turn can be parsed by the `scripts/parse_*_allocs.py`
script to find errors.

scripts/debug_heap_alloc.gdb

@@ -0,0 +1,29 @@
+das -enabled off
+break heap_allocator.cpp:81
+commands
+silent
+printf "+ %016lx %4d\n", block, length
+continue
+end
+break heap_allocator.cpp:86
+commands
+silent
+printf "+ %016lx %4d\n", block, length
+continue
+end
+break heap_allocator.cpp:120
+commands
+silent
+printf "- %016lx\n", p
+continue
+end
+break heap_allocator.cpp:140
+commands
+silent
+printf "> %016lx %4d %4d\n", p, old_length, new_length
+continue
+end
+set logging file heap_allocs.txt
+set logging overwrite on
+set logging enabled on
+continue