Add gecko glue for grid-auto-flow

[wafflespeanut]

#16024 adds parsing/serialization for grid-auto-flow. We need to add the gecko glue for it.

[wafflespeanut]

This should be pretty simple. Firstly, we should change the Mako definition for grid-auto-flow (in components/style/properties/longhands/position.rs) to have products='gecko' (so that we enable it for Stylo). Now, we should add set and copy methods manually (in gecko.mako.rs).

The first step is to add grid-auto-flow to this list, indicating that we're going manual. Then, we should add a new method set_grid_auto_flow which takes a similar signature as that of the methods that are already present there. This is the type of the value we should be comparing against while setting it in gecko. Once that's done, call the impl_simple_copy just like the surrounding methods.

If everything goes well, then ./mach build-geckolib will succeed.

[highfive]

Hi! If you have any questions regarding this issue, feel free to make a comment here, or ask it in the #servo channel in IRC.

If you intend to work on this issue, then add @highfive: assign me to your comment, and I'll assign this to you. 😄

[wafflespeanut]

@o0Ignition0o You wanna try this?

[wafflespeanut]

This is open for anyone!

[methyl]

@highfive: assign me

[highfive]

Hey @methyl! Thanks for your interest in working on this issue. It's now assigned to you!