docs: d_module_versions has an undocumented ability to accept integers

Dlang uses both integer version "levels" and arbitrary string
identifiers, and we support both, but don't mention it in the docs.

Also update a test case to pass one via declare_dependency. We already
test this kwarg for build_target.

docs/markdown/D.md

@@ -95,7 +95,7 @@ my_lib = library('mylib',
     install: true,
     version: meson.project_version(),
     soversion: project_soversion,
-    d_module_versions: ['FeatureA', 'featureB']
+    d_module_versions: ['FeatureA', 'featureB', 1]
 )
 
 pkgc = import('pkgconfig')
@@ -104,7 +104,7 @@ pkgc.generate(name: 'mylib',
               subdirs: 'd/mylib',
               version: meson.project_version(),
               description: 'A simple example D library.',
-              d_module_versions: ['FeatureA']
+              d_module_versions: ['FeatureA', 1]
 )
 install_subdir('src/mylib/', install_dir: 'include/d/mylib/')
 ```

docs/yaml/functions/_build_target_base.yaml

@@ -253,12 +253,14 @@ kwargs:
     description: When set to true, the D modules are compiled in debug mode.
 
   d_module_versions:
-    type: list[str]
+    type: list[str | int]
     description: List of module version identifiers set when compiling D sources.
 
   d_debug:
     type: list[str]
-    description: List of module debug identifiers set when compiling D sources.
+    description: |
+      The [D version identifiers](https://dlang.org/spec/version.html#version) to add
+      during the compilation of D source files.
 
   native:
     type: bool

docs/yaml/functions/declare_dependency.yaml

@@ -59,11 +59,11 @@ kwargs:
       pkg-config. *since 0.56.0* it can also be a list of `'key=value'` strings.
 
   d_module_versions:
-    type: str | list[str]
+    type: str | int | list[str | int]
     since: 0.62.0
     description: |
-      a string or a list of strings,
-      the D versions to add during the compilation of D source files
+      The [D version identifiers](https://dlang.org/spec/version.html#version) to add
+      during the compilation of D source files.
 
   d_import_dirs:
     type: list[inc | str]

test cases/d/13 declare dep/meson.build

@@ -3,7 +3,7 @@ project('meson-d-sample', 'd',
 )
 
 my_dep = declare_dependency(
-    d_module_versions: ['TestVersion'],
+    d_module_versions: ['TestVersion', 1],
     d_import_dirs: include_directories('views'),
 )