Application.mk: emit application attribute as ELF symbols

[anjiahao1]

Summary

• Emits the application's configured stack size and priority (and
  uid/gid/mode under CONFIG_SCHED_USER_IDENTITY) as absolute ELF
  symbols (nx_stacksize, nx_priority, nx_uid, nx_gid, nx_mode)
  via --defsym in MODLDFLAGS, so the NuttX binary loader can recover
  them at load time.
• Computes the symbols per target (each $(PROGLIST) entry picks up its
  own STACKSIZE_/PRIORITY_/...), and only emits a symbol when the
  application actually configures that attribute.
• Keeps the nx_* symbols through --strip-unneeded (via -K) so they
  survive in the stripped runtime image under bin/.
• Skips builtin registration for separately-built module ELFs
  (BUILD_MODULE instead of DYNLIB), matching the kernel-build model
  where apps are loaded as file ELFs.
• Related NuttX PR: binfmt: parse application stacksize/priority from ELF symbols nuttx#19440

Impact

• Is new feature added? Is existing feature changed? YES — new feature:
  application attributes are embedded as ELF symbols for the loader.
• Impact on user (will user need to adapt to change)? NO — attributes are
  only emitted when configured; otherwise behavior is unchanged.
• Impact on build (will build process change)? YES (minor) — module ELF
  links now carry --defsym nx_* flags and the stripped bin/ image
  retains those symbols.
• Impact on hardware (will arch(s) / board(s) / driver(s) change)? NO.
• Impact on documentation (is update required / provided)? NO (not yet).
• Impact on security (any sort of implications)? NO.
• Impact on compatibility (backward/forward/interoperability)? NO —
  heapsize is intentionally not emitted (depends on the separate
  task-heap feature); a typo in the original (nx_mod/wrong source) is
  fixed to nx_mode from MODE.
• Anything else to consider or add? Requires the companion NuttX PR that
  teaches binfmt/elf.c to parse these symbols.

Testing

I confirm that changes are verified on local setup and works as intended:

• Build Host(s): Ubuntu, arm-none-eabi-gcc 12.2.1
• Target(s): qemu-armv7a:knsh (CONFIG_BUILD_KERNEL), apps built from
  ../apps and mounted via hostfs as /system.
• Build: make then make install in the apps tree (kernel-build module
  ELFs).
• Run command: qemu-system-arm -semihosting -M virt -m 1024 -nographic -kernel ./nuttx

Testing logs after change (the getprime app, configured with
STACKSIZE=8192 / PRIORITY=50, carries the symbols into the stripped
runtime ELF, and the loaded task honors them):

$ arm-none-eabi-nm bin/getprime | grep nx_
00000032 A nx_priority
00002000 A nx_stacksize

nsh> getprime 4 &
  TID   PID  PPID PRI POLICY   TYPE    NPX STATE    EVENT     SIGMASK            STACK    USED FILLED COMMAND
    4     4     3  50 RR       Task      - Waiting  Semaphore 0000000000000000 0008144 0000792   9.7%  getprime 4

hello, ostest, init (NSH) all build and run; no regression on
knsh. (nx_stacksize/nx_priority are retained in bin/ after
--strip-unneeded thanks to -K.)

PR verification Self-Check

• This PR introduces only one functional change.
• I have updated all required description fields above.
• My PR adheres to Contributing Guidelines and Documentation (git commit title and message, coding standard, etc).
• My PR is still work in progress (not ready for review).
• My PR is ready for review and can be safely merged into a codebase.