perf(ui): reduce allocation overhead when encoding "redraw" events

Note for external UIs: Nvim can now emit multiple "redraw" event batches
before a final "flush" event is received. To retain existing behavior,
clients should make sure to update visible state at an explicit "flush"
event, not just the end of a "redraw" batch of event.

* Get rid of copy_object() blizzard in the auto-generated ui_event layer
* Special case "grid_line" by encoding screen state directly to
  msgpack events with no intermediate API events.
* Get rid of the arcane notion of referring to the screen as the "shell"
* Array and Dictionary are kvec_t:s, so define them as such.
* Allow kvec_t:s, such as Arrays and Dictionaries, to be allocated with
  a predetermined size within an arena.
* Eliminate redundant capacity checking when filling such kvec_t:s
  with values.

1 files changed, 4 insertions, 11 deletions

diff --git a/src/nvim/api/private/defs.h b/src/nvim/api/private/defs.h
index 396fab721d..b1e0dd364c 100644
--- a/src/nvim/api/private/defs.h
+++ b/src/nvim/api/private/defs.h
@@ -6,9 +6,10 @@
 #include <string.h>
 
 #include "nvim/func_attr.h"
+#include "nvim/lib/kvec.h"
 #include "nvim/types.h"
 
-#define ARRAY_DICT_INIT { .size = 0, .capacity = 0, .items = NULL }
+#define ARRAY_DICT_INIT KV_INITIAL_VALUE
 #define STRING_INIT { .data = NULL, .size = 0 }
 #define OBJECT_INIT { .type = kObjectTypeNil }
 #define ERROR_INIT { .type = kErrorTypeNone, .msg = NULL }
@@ -84,18 +85,10 @@ REMOTE_TYPE(Window);
 REMOTE_TYPE(Tabpage);
 
 typedef struct object Object;
-
-typedef struct {
-  Object *items;
-  size_t size, capacity;
-} Array;
+typedef kvec_t(Object) Array;
 
 typedef struct key_value_pair KeyValuePair;
-
-typedef struct {
-  KeyValuePair *items;
-  size_t size, capacity;
-} Dictionary;
+typedef kvec_t(KeyValuePair) Dictionary;
 
 typedef enum {
   kObjectTypeNil = 0,