tree-wide: extend verbs functions with extra per-verb data parameter

We often have a pattern where the same verb function is used for
multiple actions. This leads to an antipattern where we figure out what
action needs to be taken from argv[0] multiple times: often once in
parse_argv() to figure out what options are allowed, then once again
implicitly in dispatch_verb(), and then again in the action verb itself.
Let's allow passing a parameter into the verb to simplify this.

This matches a pattern we have in conf-parser.h, where we have both
void *userdata (more global) and void *data (per-config item). Here,
I opted for uintptr_t userdata. It seems that most of the time we'll
want to just pass an enum value. This works OK with no casts. I also
tried a void* and union. In both cases, much more boilerplate is needed:
either a cast or a macro to help avoid compiler warnings. uintptr_t
seems generic enough to cover foreseeable usecases with no fuss.

This is a noop refactoring. See next commit for an example.

src/bootctl/bootctl-install.c

@@ -1661,7 +1661,7 @@ static int run_install(InstallContext *c) {
         return install_variables(c, path);
 }
 
-int verb_install(int argc, char *argv[], void *userdata) {
+int verb_install(int argc, char *argv[], uintptr_t _data, void *userdata) {
         int r;
 
         /* Invoked for both "update" and "install" */
@@ -1882,7 +1882,7 @@ static int remove_loader_variables(void) {
         return r;
 }
 
-int verb_remove(int argc, char *argv[], void *userdata) {
+int verb_remove(int argc, char *argv[], uintptr_t _data, void *userdata) {
         sd_id128_t uuid = SD_ID128_NULL;
         int r;
 
@@ -1956,7 +1956,7 @@ int verb_remove(int argc, char *argv[], void *userdata) {
         return RET_GATHER(r, remove_loader_variables());
 }
 
-int verb_is_installed(int argc, char *argv[], void *userdata) {
+int verb_is_installed(int argc, char *argv[], uintptr_t _data, void *userdata) {
         int r;
 
         _cleanup_(install_context_done) InstallContext c = INSTALL_CONTEXT_NULL;