api: add vim.version (#13762)

retrun a structured version dict
:lua print(vim.inspect(vim.version()))

{
  api_compatible = 0,
  api_level = 7,
  api_prerelease = true,
  major = 0,
  minor = 5,
  patch = 0
}

runtime/doc/lua.txt

@@ -622,6 +622,9 @@ vim.api.{func}({...})					*vim.api*
         Example: call the "nvim_get_current_line()" API function: >
             print(tostring(vim.api.nvim_get_current_line()))
 
+vim.version()    					*vim.version*
+        Returns the version of the current neovim build.
+
 vim.in_fast_event()					*vim.in_fast_event()*
         Returns true if the code is executing as part of a "fast" event
         handler, where most of the API is disabled. These are low-level events

src/nvim/lua/executor.c

@@ -5,6 +5,7 @@
 #include <lualib.h>
 #include <lauxlib.h>
 
+#include "nvim/version.h"
 #include "nvim/misc1.h"
 #include "nvim/getchar.h"
 #include "nvim/garray.h"
@@ -78,6 +79,17 @@ static void nlua_error(lua_State *const lstate, const char *const msg)
   lua_pop(lstate, 1);
 }
 
+/// Return version of current neovim build
+///
+/// @param  lstate  Lua interpreter state.
+static int nlua_nvim_version(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
+{
+  Dictionary version = version_dict();
+  nlua_push_Dictionary(lstate, version, true);
+  api_free_dictionary(version);
+  return 1;
+}
+
 /// Compare two strings, ignoring case
 ///
 /// Expects two values on the stack: compared strings. Returns one of the
@@ -420,6 +432,9 @@ static int nlua_state_init(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
   // str_byteindex
   lua_pushcfunction(lstate, &nlua_str_byteindex);
   lua_setfield(lstate, -2, "str_byteindex");
+  // neovim version
+  lua_pushcfunction(lstate, &nlua_nvim_version);
+  lua_setfield(lstate, -2, "version");
   // schedule
   lua_pushcfunction(lstate, &nlua_schedule);
   lua_setfield(lstate, -2, "schedule");