meson: Provide wrap for nlohmann

Currently on the system without nlohmann installed local build fails
with error:
"""
../test/include/bej_common_test.hpp:5:10: fatal error:
nlohmann/json.hpp: No such file or directory
    5 | #include "nlohmann/json.hpp"
"""
Provide wrap file for nlohmann and add the necessary dependency to fix
the issue.

Tested:
Local build via "meson setup build && cd build && meson compile" now
finishes without errors.

Change-Id: I8d63dac6f8963c7da2c5831a1fb1998663a12f6f
Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
diff --git a/subprojects/nlohmann_json.wrap b/subprojects/nlohmann_json.wrap
new file mode 100644
index 0000000..3745380
--- /dev/null
+++ b/subprojects/nlohmann_json.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+revision = HEAD
+url = https://github.com/nlohmann/json.git
+
+[provide]
+nlohmann_json = nlohmann_json_dep
diff --git a/test/meson.build b/test/meson.build
index c61ab8c..f112e13 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -23,11 +23,13 @@
   'bej_encoder'
 ]
 
+nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
+
 libbej_test_incs = include_directories('include')
 foreach t : gtests
   test(t, executable(t.underscorify(), t + '_test.cpp',
                      build_by_default: false,
                      implicit_include_directories: false,
                      include_directories: libbej_test_incs,
-                     dependencies: [libbej, gtest, gmock]))
+                     dependencies: [libbej, gtest, gmock, nlohmann_json_dep]))
 endforeach