Canonicalize option settings earlier

[danielshahaf]

#535 / 3a7ddcd was a bug due to _zsh_highlight_load_highlighters running with the interactive environment's options. We already call emulate -L in _zsh_highlight for precisely this reason.

Long-term we should switch to an autoload design (#252), but in the interim, we should review the driver to see if we can either:

• Run more of the driver's code under canonicalized option settings; or
• Review the driver's code to see if it's robust for being run under arbitrary setopt's (particularly including those that change syntax)

[danielshahaf]

Cross-referencing #688.

[danielshahaf]

Triage: not a blocker; depends on #252/#688 which depend on redrawhook which depends on zsh-users/zsh#57; so: deferring to 0.9.0 and labeling so that once redrawhook is merged we'll re-triage this.

[danielshahaf]

Re-triaged. The dependencies #252/#688 are milestone 0.9.0, therefore so is this issue. Removing the temporary label (see previous comment).