Add injection queries for macro bodies in C and C++

crates/zed/src/languages/c/injections.scm

@@ -0,0 +1,7 @@
+(preproc_def
+    value: (preproc_arg) @content
+    (#set! "language" "c"))
+
+(preproc_function_def
+    value: (preproc_arg) @content
+    (#set! "language" "c"))

crates/zed/src/languages/cpp/injections.scm

@@ -0,0 +1,7 @@
+(preproc_def
+    value: (preproc_arg) @content
+    (#set! "language" "c++"))
+
+(preproc_function_def
+    value: (preproc_arg) @content
+    (#set! "language" "c++"))