Turn 1-line prose algorithms into step-based algorithms for readability.

[tobie]

This is especially an issue with the IDL to ES conversion algorithms.

For example, turn:

When the \[[DefineOwnProperty]] internal method of a [=named properties object=] is called,
it must return <emu-val>false</emu-val>.

into:

<div algorithm="to invoke the internal [[DefineOwnProperty]] method of named properties object">

    When the \[[DefineOwnProperty]] internal method of a [=named properties object=] is called,
    the following steps are taken:

    1.  Return <emu-val>false</emu-val>.
</div>

For context, see discussion in #198 (comment) and following comments.

[littledan]

I'm not sure if the current form is less readable. I am wondering if we should just put a <div algorithm> box around them to make it prettier.