[MesonToolchain] Added tools.build:defines conf to 'conan list' (#16228)

Addition to documentation, follow up to docs#3709

conans/model/conf.py

@@ -116,7 +116,7 @@
     "tools.build:compiler_executables": "Defines a Python dict-like with the compilers path to be used. Allowed keys {'c', 'cpp', 'cuda', 'objc', 'objcxx', 'rc', 'fortran', 'asm', 'hip', 'ispc', 'ld', 'ar'}",
     "tools.build:cxxflags": "List of extra CXX flags used by different toolchains like CMakeToolchain, AutotoolsToolchain and MesonToolchain",
     "tools.build:cflags": "List of extra C flags used by different toolchains like CMakeToolchain, AutotoolsToolchain and MesonToolchain",
-    "tools.build:defines": "List of extra definition flags used by different toolchains like CMakeToolchain and AutotoolsToolchain",
+    "tools.build:defines": "List of extra definition flags used by different toolchains like CMakeToolchain, AutotoolsToolchain and MesonToolchain",
     "tools.build:sharedlinkflags": "List of extra flags used by CMakeToolchain for CMAKE_SHARED_LINKER_FLAGS_INIT variable",
     "tools.build:exelinkflags": "List of extra flags used by CMakeToolchain for CMAKE_EXE_LINKER_FLAGS_INIT variable",
     "tools.build:linker_scripts": "List of linker script files to pass to the linker used by different toolchains like CMakeToolchain, AutotoolsToolchain, and MesonToolchain",