Eliminate the termsize handling from common.h

Finish the transition to termsize.h. Remove the scary termsize bits
from common.cpp, which can throw off events at arbitrary calls and are
dangerously reentrant. Migrate everyone to the new termsize.h.

src/env_dispatch.cpp

@@ -51,6 +51,7 @@
 #include "proc.h"
 #include "reader.h"
 #include "screen.h"
+#include "termsize.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 #define DEFAULT_TERM1 "ansi"
@@ -231,8 +232,7 @@ static void handle_change_ambiguous_width(const env_stack_t &vars) {
 }
 
 static void handle_term_size_change(const env_stack_t &vars) {
-    UNUSED(vars);
-    invalidate_termsize(true);  // force fish to update its idea of the terminal size plus vars
+    termsize_container_t::shared().handle_columns_lines_var_change(vars);
 }
 
 static void handle_fish_history_change(const env_stack_t &vars) {