compat internal types: import and re-export PreactElement

[henryqdineen]

Since PreactElement is used in this module we should also import it instead of only doing the export {} from.

https://github.com/henryqdineen/preact/blob/a1309b8e1a51ee51ca93848d69dc30a5d3ad0356/compat/src/internal.d.ts#L25

I understand that these are just internal types that are used for ts-check but it was just something that I noticed. It seems like it has been innocuous so far. Thanks!

[rschristian]

Sorry this was missed and sat for so long

[coveralls]

coverage: 99.605%. remained the same
when pulling cab57f2 on henryqdineen:hqd-compat-types
into e2c8a45 on preactjs:main.