BLD: use meson-native dependency lookup for pybind11

This makes use of mesonbuild/meson#11463 to find
pybind11 using the pybind11-config script installed in build isolation.

If that doesn't work, for example the version of Meson is too old, then
we fall back to the previous method of manually running some
introspection code, and no harm is done.

scipy/meson.build

@@ -80,22 +80,27 @@ npymath_lib = cc.find_library('npymath', dirs: npymath_path)
 npyrandom_lib = cc.find_library('npyrandom', dirs: npyrandom_path)
 
 # pybind11 include directory - needed in several submodules
-incdir_pybind11 = run_command(py3,
-  [
-    '-c',
-    '''from os.path import relpath
-import pybind11
-try:
-  incdir = relpath(pybind11.get_include())
-except Exception:
-  incdir = pybind11.get_include()
-print(incdir)
-'''
-  ],
-  check: true
-).stdout().strip()
+#
+# in meson 1.1.0, this will find the pyproject.toml build-requires version
+pybind11_dep = dependency('pybind11', version: '>=2.10.0', required: false, allow_fallback: true)
+if not pybind11_dep.found()
+  incdir_pybind11 = run_command(py3,
+    [
+      '-c',
+      '''from os.path import relpath
+  import pybind11
+  try:
+    incdir = relpath(pybind11.get_include())
+  except Exception:
+    incdir = pybind11.get_include()
+  print(incdir)
+  '''
+    ],
+    check: true
+  ).stdout().strip()
 
-pybind11_dep = declare_dependency(include_directories: incdir_pybind11)
+  pybind11_dep = declare_dependency(include_directories: incdir_pybind11)
+endif
 
 # Pythran include directory and build flags
 if use_pythran