[simd.syn] Wrong formatting in synopsis

[Eisenwave]

The synopsis for in [simd.syn] goes against our usual formatting conventions in a few ways:

• Some of the section comments (e.g. // [simd.bit], Bit manipulation) have a capitalized title. To my knowledge, it should be bit manipulation.
• assoc_laguerre and assoc_legendre have improperly aligned parameters.
• lerp and a few other functions do not correctly indent the function name when the previous line is dedicated to a return type.

There are also some things that are not incorrect, but very ugly, like:

  template<simd-type V>
    constexpr rebind_t<make_signed_t<typename V::value_type>, V>
    countl_zero(const V& v) noexcept;
  template<simd-type V>
    constexpr rebind_t<make_signed_t<typename V::value_type>, V> countl_one(const V& v) noexcept;

countl_zero is not properly indented, but that's not what I'm pointing out here. Rather, countl_one is put all on one line solely because it's one character shorter. I think it would be much less ugly if we formatted countl_zero and countl_one the same.

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Obviously, any such fixups should be done after post-Sofia motions.