c-api: support IWYU pragmas (#7473)

This allows clangd to not import the headers in the wasmtime directory,
as not all of them include their dependencies correctly. This means that
clangd can import a header directly and it breaks the build, as the
order `wasmtime.h` #includes is important.

See: https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/IWYUPragmas.md

Signed-off-by: Tyler Rockwood <rockwood@redpanda.com>

crates/c-api/include/wasmtime.h

@@ -181,6 +181,7 @@
 #define WASMTIME_API_H
 
 #include <wasi.h>
+// IWYU pragma: begin_exports
 #include <wasmtime/config.h>
 #include <wasmtime/engine.h>
 #include <wasmtime/error.h>
@@ -196,6 +197,7 @@
 #include <wasmtime/trap.h>
 #include <wasmtime/val.h>
 #include <wasmtime/async.h>
+// IWYU pragma: end_exports
 
 /**
  * \brief Wasmtime version string.