Support keeping a leader together with the word before it

[bertfrees]

In all the cases below, the leader should not be separated from the word before it:

<obfl>
  <layout-master name="body" page-width="10" page-height="5" duplex="true">
    <default-template>
      <header/>
      <footer/>
    </default-template>
  </layout-master>
  <sequence master="body">
    <block>
      ⠤⠤⠤ ⠤⠤⠤⠤<leader pattern="⠁" position="100%" align="right"/>⠿⠿⠿
    </block>

In the following two examples, there is a space after the leader, but a leader is always kept together with the content after it.

    <block>
      ⠤⠤⠤ ⠤⠤⠤⠤<leader pattern="⠁" position="100%" align="right"/> ⠿⠿⠿
    </block>
    <block>
      ⠤⠤⠤ ⠤⠤⠤<leader pattern="⠁" position="100%" align="right"/> ⠿⠿⠿
    </block>

In this last example, the space before the leader is a non-breaking one.

    <block>
      ⠤⠤⠤ ⠤⠤⠤ <leader pattern="⠁" position="100%" align="right"/> ⠿⠿⠿
    </block>
  </sequence>
</obfl>