Refactor code structure for improved readability and maintainability

libsrtp/include/srtp3/meson.build

@@ -0,0 +1,7 @@
+# Copy public headers scattered across the source tree into a single directory
+# so that we can use it in declare_dependency()
+foreach h : public_headers
+  configure_file(input: h,
+    output: '@BASENAME@.h',
+    copy: true)
+endforeach