vim-patch:8.1.1693: syntax coloring and highlighting is in one big file (#17721)

Problem:    Syntax coloring and highlighting is in one big file.
Solution:   Move the highlighting to a separate file. (Yegappan Lakshmanan,
            closes vim/vim#4674)

f9cc9f209e

Name the new file highlight_group.c instead.

Co-authored-by: zeertzjq <zeertzjq@outlook.com>

src/nvim/syntax.h

@@ -29,12 +29,6 @@
 
 #define SYN_GROUP_STATIC(s) syn_check_group(S_LEN(s))
 
-typedef struct {
-  char *name;
-  RgbValue color;
-} color_name_table_T;
-extern color_name_table_T color_name_table[];
-
 /// Array of highlight definitions, used for unit testing
 extern const char *const highlight_init_cmdline[];