refactor: replace USE_X11 with OS_LINUX for sharing code with Ozone

[modembcc]

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 referenced patches demonstrate the specific code changes needed to replace X11-specific conditionals with Linux-wide ones, enabling Wayland support while maintaining existing X11 functionality.

#2 going away

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

#3 commit guidelines

🔍 This pull request is a small first step toward bringing Wayland support to Electron by replacing the USE_X11 macro with OS_LINUX to allow sharing code with the Ozone platform.

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

🔍 The contributor guidelines outline the expected code of conduct and contribution process for the Electron project.

#5 chromium#1085700

🔍 The USE_X11 macro is being replaced with OS_LINUX to enable sharing code across X11 and Wayland (Ozone) builds, as part of the initial step toward Wayland support in Electron.

#6 these chromium changes

🔍 The webpage describes Gerrit Code Review, which is a web-based code review system for Git repositories, but the relevant insight for this PR is that the USE_X11 macro is being replaced with OS_LINUX to enable sharing code with Ozone, which is a necessary step for supporting Wayland in