refactor: replace USE_X11 with OS_LINUX for sharing code with Ozone

[jdanceze]

Description of Change

This pull-request is a small first step in trying to bring support for Wayland to Electron. I'm planning to follow up on this with more pull-requests in an effort to upstream these Wayland patches.

However, those patches will need some adjustments in order to make them compatible with the upcoming Chromium changes (chromium#1085700) which will soon be merged into Electron (#25488). In particular, it should be taken into consideration that the USE_X11 and USE_OZONE build flags are no longer mutually exclusive.

Also, USE_X11 is going away so it might be desirable as a long term goal to remove it from Electron too and replace it with the Ozone equivalents.

With that in mind, this pull-request replaces a few instances of #if defined(USE_X11) with #if defined(OS_LINUX) where it was identified that the guarded code could be shared with Ozone.

The more meaningful changes will come in the upcoming pull-requests but I'll be waiting for these chromium changes to be pulled into Electron first (#24984, #25488).

Checklist

• PR description included and stakeholders cc'd (@zcbenz @hedgepigdaniel)
• npm test passes
• PR title follows semantic commit guidelines

Release Notes

Notes: none

[MonnetalX]

🔍 PR Link Analysis

🔗 Ranked Links

#1 these Wayland patches

🔍 The linked comparison shows the upstream Wayland patches that this PR aims to incrementally port, specifically replacing USE_X11 with OS_LINUX guards to share code between X11 and Ozone builds.

#2 going away

🔍 The issue requests prebuilt Electron binaries for Wayland, as current Linux builds rely on X11/GTK and perform poorly on embedded devices using Wayland.

#3 commit guidelines

🔍 This pull request replaces USE_X11 with OS_LINUX to enable sharing code between X11 and Wayland builds, as part of a broader effort to bring Wayland support to Electron.

#4 https://github.com/electron/electron/blob/master/CONTRIBUTING.md

🔍 The contributor guidelines outline the process for proposing changes to Electron, including the expectation that contributors follow the code of conduct and that bug reports are closed if inactive for supported versions.

#5 chromium#1085700

🔍 The webpage explains that replacing USE_X11 with OS_LINUX allows code to be shared between X11 and Wayland (Ozone) builds, which is the first step toward adding Wayland support to Electron.

#6 these chromium changes

🔍 The webpage describes Gerrit's code review system, which is relevant to the PR's goal of upstreaming Wayland patches through a structured review process.