Update `freetype-sys` to 0.23

[simonwuelker]

Servo is currently using 0.20 which has multiple soundness holes. (For example, https://docs.rs/freetype-sys/0.20.1/freetype_sys/fn.FT_HAS_MULTIPLE_MASTERS.html should be unsafe).

This also requires us to bump freetype-sys in the following servo-owned crates:

• harfbuzz-sys
• freetype

This is slightly inconvenient: Bumping freetype-sys is a breaking change, as only a single dependency can link to freetype at a time. Thus, any user of the crates above would have to update as well.

[atouchet]

freetype-sys was updated to 0.23 in harfbuzz-sys in servo/rust-harfbuzz#270. If a new breaking harfbuzz-sys version is released ideally the core-graphics, core-text (after servo/core-foundation-rs#738 is merged), and windows dependencies should be updated beforehand as well.