string-table: Introduce DECLARE_STRING_TABLE_LOOKUP() and friends

Let's introduce these for the following two reasons:
- Using them makes sure the parameter names match between declaration
  and definition (if both use the corresponding macros).
- They make sure developers can't forget the _const_ and _pure_
  attributes for the declarations.

This commit also includes some include sorting fixes

src/shared/kernel-image.h

@@ -12,7 +12,7 @@ typedef enum KernelImageType {
         _KERNEL_IMAGE_TYPE_INVALID = -EINVAL,
 } KernelImageType;
 
-const char* kernel_image_type_to_string(KernelImageType t) _const_;
+DECLARE_STRING_TABLE_LOOKUP_TO_STRING(kernel_image_type, KernelImageType);
 
 int inspect_kernel(
                 int dir_fd,