bug#49629: 27.2; electric-pair-mode doesn't work for angle brackets in HTML file

[Stefan Monnier]

> FIrst, changing `syntax-propertize-function` from nil to `ignore` was wrong
> IIUC.  If the function is set, then it is wholly responsible for applying
> syntax table.  When set to nil the default behavior is used, but when set
> to `ignore`, that should mean that no syntax is applied at all.  In
> practice, I don't know what behavior that causes.

The two behave identically (IOW the "default behavior" is the same as
that of `ignore`).

> Second, since `electric-pair--with-uncached-syntax` appears to be used for
> doing text-mode matching (as you've also observed), maybe we should
> de-generalize it to do only that.  I think that allows us to make some
> simplifying assumptions about the state of the world.

Sounds good.


        Stefan