code: public T withImports(SymbolTable... imports)
      {
          T b = mutable();
          b.setImports(imports);
          return b;
      }
docs: Declares the imports to use when building an {@link IonWriter},
  returning a new mutable builder if this is immutable.
  <p>
  If the imports sequence is not null and not empty, the output stream
  will be bootstrapped with a local symbol table that uses the given
  {@code imports}.
  
  @param imports a sequence of shared symbol tables.
  The first (and only the first) may be a system table.
  
  @return this instance, if mutable;
  otherwise a mutable copy of this instance.
  
  @see #getImports()
  @see #setImports(SymbolTable...)