meson: adjust nlohmann-json dependency

The meson dependency for nlohmann-json can be simplified quite
a bit from what some repositories are doing.  Use the simplest
form of the dependency and rename the wrap file for consistency.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I51ecfabc37d4023b33b72e558a5a65f97ae303fd
diff --git a/subprojects/nlohmann_json.wrap b/subprojects/nlohmann_json.wrap
index dbdadd5..3745380 100644
--- a/subprojects/nlohmann_json.wrap
+++ b/subprojects/nlohmann_json.wrap
@@ -1,3 +1,6 @@
 [wrap-git]
 revision = HEAD
 url = https://github.com/nlohmann/json.git
+
+[provide]
+nlohmann_json = nlohmann_json_dep