luci-compat: update markup for CBI TableSections

Update legacy CBI markup to use actual table, tr, th and td elements
instead of using div element corresponding table classes.

Fixes compatibility with OpenWrt 2020 theme.

Ref: https://github.com/openwrt/luci/issues/4972
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-compat/luasrc/view/cbi/cell_valuefooter.htm

@@ -1,2 +1,2 @@
 </div>
-</div>
+</td>

modules/luci-compat/luasrc/view/cbi/cell_valueheader.htm

@@ -3,7 +3,7 @@
 	local descr = luci.util.trim(striptags(self.description))
 	local ftype = self.typename or (self.template and self.template:gsub("^.+/", ""))
 -%>
-<div class="td cbi-value-field<% if self.error and self.error[section] then %> cbi-value-error<% end %><% if self.password then %> nowrap<% end %>"<%=
+<td class="td cbi-value-field<% if self.error and self.error[section] then %> cbi-value-error<% end %><% if self.password then %> nowrap<% end %>"<%=
 	attr("data-name", self.option) ..
 	ifattr(ftype and #ftype > 0, "data-widget", ftype) ..
 	ifattr(title and #title > 0, "data-title", title, true) ..

modules/luci-compat/luasrc/view/cbi/tblsection.htm

@@ -46,12 +46,12 @@ function render_titles()
 		return
 	end
 
-	%><div class="tr cbi-section-table-titles <%=anonclass%>"<%=titlename%>><%
+	%><tr class="tr cbi-section-table-titles <%=anonclass%>"<%=titlename%>><%
 
 	local i, k
 	for i, k in ipairs(self.children) do
 		if not k.optional then
-			%><div class="th cbi-section-table-cell"<%=
+			%><th class="th cbi-section-table-cell"<%=
 				width(k) .. attr('data-widget', k.typename) %>><%
 
 			if k.titleref then
@@ -64,15 +64,15 @@ function render_titles()
 				%></a><%
 			end
 
-			%></div><%
+			%></th><%
 		end
 	end
 
 	if self.sortable or self.extedit or self.addremove then
-		%><div class="th cbi-section-table-cell cbi-section-actions"></div><%
+		%><th class="th cbi-section-table-cell cbi-section-actions"></th><%
 	end
 
-	%></div><%
+	%></tr><%
 
 	rowcnt = rowcnt + 1
 end
@@ -82,25 +82,25 @@ function render_descriptions()
 		return
 	end
 
-	%><div class="tr cbi-section-table-descr <%=anonclass%>"><%
+	%><tr class="tr cbi-section-table-descr <%=anonclass%>"><%
 
 	local i, k
 	for i, k in ipairs(self.children) do
 		if not k.optional then
-			%><div class="th cbi-section-table-cell"<%=
+			%><th class="th cbi-section-table-cell"<%=
 				width(k) .. attr("data-widget", k.typename) %>><%
 
 			write(k.description)
 
-			%></div><%
+			%></th><%
 		end
 	end
 
 	if self.sortable or self.extedit or self.addremove then
-		%><div class="th cbi-section-table-cell cbi-section-actions"></div><%
+		%><th class="th cbi-section-table-cell cbi-section-actions"></th><%
 	end
 
-	%></div><%
+	%></tr><%
 
 	rowcnt = rowcnt + 1
 end
@@ -116,7 +116,7 @@ end
 		<input type="hidden" id="cbi.sts.<%=self.config%>.<%=self.sectiontype%>" name="cbi.sts.<%=self.config%>.<%=self.sectiontype%>" value="" />
 	<%- end -%>
 	<div class="cbi-section-descr"><%=self.description%></div>
-	<div class="table cbi-section-table">
+	<table class="table cbi-section-table">
 		<%-
 			render_titles()
 			render_descriptions()
@@ -134,7 +134,7 @@ end
 					valuefooter = "cbi/cell_valuefooter"
 				}
 		-%>
-		<div class="tr cbi-section-table-row<%=colorclass%>" id="cbi-<%=self.config%>-<%=section%>"<%=sectiontitle%>>
+		<tr class="tr cbi-section-table-row<%=colorclass%>" id="cbi-<%=self.config%>-<%=section%>"<%=sectiontitle%>>
 			<%-
 				local node
 				for k, node in ipairs(self.children) do
@@ -145,7 +145,7 @@ end
 			-%>
 
 			<%- if self.sortable or self.extedit or self.addremove then -%>
-				<div class="td cbi-section-table-cell nowrap cbi-section-actions">
+				<td class="td cbi-section-table-cell nowrap cbi-section-actions">
 					<div>
 						<%- if self.sortable then -%>
 							<input class="btn cbi-button cbi-button-up" type="button" value="<%:Up%>" onclick="return cbi_row_swap(this, true, 'cbi.sts.<%=self.config%>.<%=self.sectiontype%>')" title="<%:Move up%>" />
@@ -162,17 +162,17 @@ end
 							<input class="btn cbi-button cbi-button-remove" type="submit" value="<%:Delete%>"  onclick="this.form.cbi_state='del-section'; return true" name="cbi.rts.<%=self.config%>.<%=k%>" alt="<%:Delete%>" title="<%:Delete%>" />
 						<%- end -%>
 					</div>
-				</div>
+				</td>
 			<%- end -%>
-		</div>
+		</tr>
 		<%- end -%>
 
 		<%- if isempty then -%>
-		<div class="tr cbi-section-table-row placeholder">
+		<tr class="tr cbi-section-table-row placeholder">
-			<div class="td"><em><%:This section contains no values yet%></em></div>
+			<td class="td"><em><%:This section contains no values yet%></em></td>
-		</div>
+		</tr>
 		<%- end -%>
-	</div>
+	</table>
 
 	<% if self.error then %>
 		<div class="cbi-section-error">