libc: implement vscanf()

[abrarnasirjaffari]

This pull request implements the vscanf() function in Zephyr's libc. The implementation provides a minimal version by delegating to vfscanf() with stdin as the input stream, in accordance with the C89 standard.

Changes Included:

• Source Code:
  A new implementation of vscanf() has been added in lib/libc/stdio/vscanf.c:

  /*
   * Copyright The Zephyr Project Contributors
   *
   * SPDX-License-Identifier: Apache-2.0
   */
  
  #include <stdio.h>
  #include <stdarg.h>
  
  FILE *vscanf(const char *format, va_list args)
  {
      return vfscanf(stdin, format, args);
  }
• Build System:
  The build configuration in lib/libc/stdio/CMakeLists.txt has been updated to include vscanf.c.

Verification:

• A pristine build was performed using:

  west build -t pristine -b qemu_x86 samples/hello_world
• The sample application was run using:

  west build -t run -b qemu_x86 samples/hello_world

Additional Notes:

• This change addresses issue [#66954](libc: implement vscanf() #66954).
• The commit message follows Zephyr's commit guidelines, including the necessary Signed-off-by line for DCO compliance.

[DanTGL]

• Add a license header
• Format the file
• Sign the commits
• Make sure every commit passes all of the checks
• Write a description for the commits
• Run checks locally before pushing

Please read https://docs.zephyrproject.org/latest/contribute/guidelines.html

[cfriedt]

@abrarnasirjaffari - it looks like the 4 commits should probably be squashed.

[abrarnasirjaffari]

@cfriedt Please help me with the check that is failing. I am not sure how to resolve it. Failing check is Compliance Checks / Run compliance checks on patch series (PR) (pull_request)