Appends a compile-time-constant string, which will
not be escaped.
Important: For this class to be able to honor its contract as required by {@link SafeHtml}, all uses of this method must satisfy the following constraints:
- The argument expression must be fully determined at compile time.
- The value of the argument must end in "inner HTML" context and not contain incomplete HTML tags. I.e., the following is not a correct use of this method, because the {@code } tag is incomplete:
{@code shb.appendHtmlConstant("