Describe the bug
meson format sorts the files in files() by default, but doesn't follow the instructions in the Meson style guide.

To Reproduce
Run meson format meson.build, where meson.build is:

project('a')
sources = files(
    'aaa/a1.c',
    'aaa/a2.c',
    'bbb/subdir1/b1.c',
    'bbb/subdir2/b2.c',
    'bbb/subdir10/b3.c',
    'bbb/subdir20/b4.c',
    'bbb/b5.c',
    'bbb/b6.c',
    'f1.c',
    'f2.c',
    'f10.c',
    'f20.c',
)

This produces:

project('a')
sources = files(
    'aaa/a1.c',
    'aaa/a2.c',
    'bbb/b5.c',
    'bbb/b6.c',
    'bbb/subdir1/b1.c',
    'bbb/subdir10/b3.c',
    'bbb/subdir2/b2.c',
    'bbb/subdir20/b4.c',
    'f1.c',
    'f10.c',
    'f2.c',
    'f20.c',
)

Expected behavior
The output matches the input.

system parameters

• Is this a cross build or just a plain native build (for the same computer)?
  native

• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
  Fedora 42

• what Python version are you using e.g. 3.8.0
  3.13.7

• what meson --version
  1.9.0

• what ninja --version if it's a Ninja build
  1.12.1