refactor: replace USE_X11 with OS_LINUX for sharing code with Ozone

[c4rtune]

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 patches demonstrate the necessary code changes to replace USE_X11 with OS_LINUX conditionals, enabling shared code paths for Wayland/Ozone support in Electron.

#2 #25488

🔍 Replacing USE_X11 with OS_LINUX enables sharing code across X11 and Wayland backends in Electron.

#3 going away

🔍 This pull request replaces USE_X11 with OS_LINUX to enable sharing code with Ozone, which is a necessary step for supporting Wayland on Linux.

#4 #24984

🔍 Replacing USE_X11 with OS_LINUX enables sharing code with Ozone, which is a necessary step toward supporting Wayland in Electron.

#5 commit guidelines

🔍 This pull request replaces USE_X11 with OS_LINUX to enable sharing code with Ozone, which is a necessary step for supporting Wayland in Electron.

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

🔍 The CONTRIBUTING.md outlines the project's guidelines for contributions, including the expectation to uphold the code of conduct and the process for reporting issues.

#7 chromium#1085700

🔍 The webpage explains that USE_X11 is a build flag specific to X11, while OS_LINUX is a more general platform flag that can be used to share code across both X11 and Wayland (Ozone) builds on Linux.

#8 these chromium changes

🔍 The webpage discusses Gerrit Code Review, which is relevant to the PR's goal of sharing code across different display servers like X11 and Wayland.