Create lightweight forks of text/template and html/template

This commit also removes support for Ace and Amber templates.

Updates #6594

tpl/internal/go_templates/htmltemplate/delim_string.go

@@ -0,0 +1,16 @@
+// Code generated by "stringer -type delim"; DO NOT EDIT.
+
+package template
+
+import "strconv"
+
+const _delim_name = "delimNonedelimDoubleQuotedelimSingleQuotedelimSpaceOrTagEnd"
+
+var _delim_index = [...]uint8{0, 9, 25, 41, 59}
+
+func (i delim) String() string {
+	if i >= delim(len(_delim_index)-1) {
+		return "delim(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _delim_name[_delim_index[i]:_delim_index[i+1]]
+}