patch 9.0.0007: no support for double, dotted and dashed underlines

Problem:    No support for double, dotted and dashed underlines.
Solution:   Add the termcap entries and highlight modes. (closes #9553)
diff --git a/src/screen.c b/src/screen.c
index 82a0e91..0151888 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -1855,8 +1855,17 @@
 		out_str(T_SO);
 	    if ((attr & HL_UNDERCURL) && *T_UCS != NUL) // undercurl
 		out_str(T_UCS);
-	    if (((attr & HL_UNDERLINE)	    // underline or undercurl
-			|| ((attr & HL_UNDERCURL) && *T_UCS == NUL))
+	    if ((attr & HL_UNDERDOUBLE) && *T_USS != NUL) // double underline
+		out_str(T_USS);
+	    if ((attr & HL_UNDERDOTTED) && *T_DS != NUL) // dotted underline
+		out_str(T_DS);
+	    if ((attr & HL_UNDERDASHED) && *T_CDS != NUL) // dashed underline
+		out_str(T_CDS);
+	    if (((attr & HL_UNDERLINE)	    // underline or undercurl, etc.
+			|| ((attr & HL_UNDERCURL) && *T_UCS == NUL)
+			|| ((attr & HL_UNDERDOUBLE) && *T_USS == NUL)
+			|| ((attr & HL_UNDERDOTTED) && *T_DS == NUL)
+			|| ((attr & HL_UNDERDASHED) && *T_CDS == NUL))
 		    && *T_US != NUL)
 		out_str(T_US);
 	    if ((attr & HL_ITALIC) && *T_CZH != NUL)	// italic
@@ -1951,6 +1960,8 @@
 	else
 #endif
 	{
+	    int is_under;
+
 	    if (screen_attr > HL_ALL)			// special HL attr.
 	    {
 		attrentry_T *aep;
@@ -2030,15 +2041,16 @@
 		else
 		    out_str(T_SE);
 	    }
-	    if ((screen_attr & HL_UNDERCURL) && *T_UCE != NUL)
+	    is_under = (screen_attr & (HL_UNDERCURL
+			  | HL_UNDERDOUBLE | HL_UNDERDOTTED | HL_UNDERDASHED));
+	    if (is_under && *T_UCE != NUL)
 	    {
 		if (STRCMP(T_UCE, T_ME) == 0)
 		    do_ME = TRUE;
 		else
 		    out_str(T_UCE);
 	    }
-	    if ((screen_attr & HL_UNDERLINE)
-			    || ((screen_attr & HL_UNDERCURL) && *T_UCE == NUL))
+	    if ((screen_attr & HL_UNDERLINE) || (is_under && *T_UCE == NUL))
 	    {
 		if (STRCMP(T_UE, T_ME) == 0)
 		    do_ME = TRUE;