meson: Add missing dependencies for utility files for gdbus-codegen

Various parts of the build (such as `objectmanager-rst-gen`) depend on
running `gdbus-codegen` after it’s been built, but they currently only
encode a dependency to the main codegen Python file and not the
supporting files. This can cause `gdbus-codegen` to fail with an
`ImportError` if the build races so that `objectmanager-rst-gen` is
built before the codegen supporting files.

Example failure here: https://gitlab.gnome.org/pwithnall/glib/-/jobs/3266471
```
FAILED: gio/tests/gdbus-object-manager-example/objectmanager-rst-gen-org.gtk.GDBus.Example.ObjectManager.Animal.rst gio/tests/gdbus-object-manager-example/objectmanager-rst-gen-org.gtk.GDBus.Example.ObjectManager.Cat.rst
/usr/bin/python3 gio/gdbus-2.0/codegen/gdbus-codegen --interface-prefix org.gtk.GDBus.Example.ObjectManager. --generate-rst objectmanager-rst-gen --output-directory gio/tests/gdbus-object-manager-example ../gio/tests/gdbus-object-manager-example/gdbus-example-objectmanager.xml
Traceback (most recent call last):
  File "/builds/pwithnall/glib/_build/gio/gdbus-2.0/codegen/gdbus-codegen", line 53, in <module>
    from codegen import codegen_main
  File "/builds/pwithnall/glib/_build/gio/gdbus-2.0/codegen/codegen_main.py", line 29, in <module>
    from . import dbustypes
  File "/builds/pwithnall/glib/_build/gio/gdbus-2.0/codegen/dbustypes.py", line 22, in <module>
    from . import utils
ImportError: cannot import name 'utils' from 'codegen' (/builds/pwithnall/glib/_build/gio/gdbus-2.0/codegen/__init__.py)
```

Signed-off-by: Philip Withnall <philip@tecnocode.co.uk>

gio/tests/gdbus-object-manager-example/meson.build

@@ -20,7 +20,10 @@ gdbus_example_objectmanager_generated = custom_target('objectmanager-gen',
              '--generate-docbook', 'objectmanager-gen',
              '--symbol-decorator', 'GDBUS_OBJECT_MANAGER_EXAMPLE_AVAILABLE_IN_ALL',
              '--symbol-decorator-header', 'gdbus-example-objectmanager-visibility.h',
-             '@INPUT@'])
+             '@INPUT@'],
+  depend_files : gdbus_codegen_built_files,
+  depends : gdbus_codegen_built_targets,
+)
 
 gdbus_example_objectmanager_rst_gen = custom_target('objectmanager-rst-gen',
   input: gdbus_example_objectmanager_xml,
@@ -36,6 +39,8 @@ gdbus_example_objectmanager_rst_gen = custom_target('objectmanager-rst-gen',
     '--output-directory', '@OUTDIR@',
     '@INPUT@',
   ],
+  depend_files: gdbus_codegen_built_files,
+  depends: gdbus_codegen_built_targets,
 )
 
 extra_c_args = []

gio/tests/meson.build

@@ -373,6 +373,7 @@ if host_machine.system() != 'windows'
         output :  ['gdbus-test-codegen-generated.h',
                    'gdbus-test-codegen-generated.c'],
         depend_files : gdbus_codegen_built_files,
+        depends : gdbus_codegen_built_targets,
         command : [python, gdbus_codegen,
                    '--interface-prefix', 'org.project.',
                    '--output-directory', '@OUTDIR@',
@@ -389,6 +390,7 @@ if host_machine.system() != 'windows'
         output :  ['gdbus-test-codegen-generated-min-required-2-64.h',
                    'gdbus-test-codegen-generated-min-required-2-64.c'],
         depend_files : gdbus_codegen_built_files,
+        depends : gdbus_codegen_built_targets,
         command : [python, gdbus_codegen,
                    '--glib-min-required', '2.64',
                    '--interface-prefix', 'org.project.',
@@ -405,6 +407,7 @@ if host_machine.system() != 'windows'
           input :   ['test-codegen.xml'],
           output :  ['gdbus-test-codegen-generated-interface-info.h'],
           depend_files : gdbus_codegen_built_files,
+          depends : gdbus_codegen_built_targets,
           command : [python, gdbus_codegen,
                      '--interface-info-header',
                      annotate_args,
@@ -414,6 +417,7 @@ if host_machine.system() != 'windows'
           input :   ['test-codegen.xml'],
           output :  ['gdbus-test-codegen-generated-interface-info.c'],
           depend_files : gdbus_codegen_built_files,
+          depends : gdbus_codegen_built_targets,
           command : [python, gdbus_codegen,
                      '--interface-info-body',
                      annotate_args,
@@ -528,6 +532,7 @@ if host_machine.system() != 'windows'
         output :  ['fake-document-portal-generated.h',
                    'fake-document-portal-generated.c'],
         depend_files : gdbus_codegen_built_files,
+        depends : gdbus_codegen_built_targets,
         command : [python, gdbus_codegen,
                    '--interface-prefix', 'org.freedesktop.portal.',
                    '--output-directory', '@OUTDIR@',