Add reader flog category

For both input and reader, because the "reader" term is more general
and we don't have enough messages to justify multiple categories

src/flog.h

@@ -92,6 +92,8 @@ class category_list_t {
     category_t iothread{L"iothread", L"Background IO thread events"};
 
     category_t term_support{L"term-support", L"Terminal feature detection"};
+
+    category_t reader{L"reader", L"The interactive reader/input system"};
 };
 
 /// The class responsible for logging.

src/input.cpp

@@ -458,7 +458,7 @@ void inputter_t::mapping_execute_matching_or_generic(bool allow_commands) {
     if (auto mapping = find_mapping()) {
         mapping_execute(*mapping, allow_commands);
     } else {
-        debug(2, L"no generic found, ignoring char...");
+        FLOGF(reader, L"no generic found, ignoring char...");
         auto evt = event_queue_.readch();
         if (evt.is_eof()) {
             event_queue_.push_front(evt);

src/input_common.cpp

@@ -24,6 +24,7 @@
 #include "env.h"
 #include "env_universal_common.h"
 #include "fallback.h"  // IWYU pragma: keep
+#include "flog.h"
 #include "global_safety.h"
 #include "input_common.h"
 #include "iothread.h"
@@ -188,7 +189,7 @@ char_event_t input_event_queue_t::readch() {
         switch (sz) {
             case static_cast<size_t>(-1): {
                 std::memset(&state, '\0', sizeof(state));
-                debug(2, L"Illegal input");
+                FLOG(reader, L"Illegal input");
                 return char_event_type_t::check_exit;
             }
             case static_cast<size_t>(-2): {

src/reader.cpp

@@ -3311,7 +3311,7 @@ maybe_t<wcstring> reader_data_t::readline(int nchars_or_0) {
             } else {
                 // This can happen if the user presses a control char we don't recognize. No
                 // reason to report this to the user unless they've enabled debugging output.
-                debug(2, _(L"Unknown key binding 0x%X"), c);
+                FLOGF(reader, _(L"Unknown key binding 0x%X"), c);
             }
             rls.last_cmd = none();
         }