[scripts] Add symbol table building script

Create a script that builds a simple-to-read symbol table from the
output of `nm`. Include running that script over the kernel in the
build, and including that output in the initrd.

Tags: callstack debugging

assets/initrd.toml

@@ -12,6 +12,10 @@
 dest = "screenfont.psf"
 source = "../assets/fonts/tamsyn8x16r.psf"
 
+[[files]]
+dest = "symbol_table.dat"
+source = "symbol_table.dat"
+
 [[files]]
 dest = "nulldrv1"
 source = "user/nulldrv"