fix: expose libgtkui::GetFgColor (backport: 3-1-x)

[Cobinja]

Description of Change

Backport libcc portion of https://github.com/electron/electron/pull/15878 to 3-1-x /cc @inukshuk

Checklist

• [x] PR description included and stakeholders cc'd
• [x] Patch information is added to appropriate .patches.yaml
• [x] script/update runs without error
• [x] PR title follows semantic commit guidelines

Notes

srcipt/updateruns into the (probably) same error as in https://github.com/electron/libchromiumcontent/pull/690#issuecomment-424504022 The patch file actually gets applied, but the script tells otherwise

[codebytere]

hey @Cobinja this patch doesn't apply due to mismatched line numbers; you'll need to ensure it applies locally with script/update. We can get this merged once that's fixed up!

[Cobinja]

@codebytere I forced-pushed a new version. It wasn't the line numbers you suspected. I can't tell what it actually was but I suspect a confusion of line-ending types