Wrap EGL image usage in a GObject

[robert-ancell]

This ensures it is destroyed when no object is using it. It was previously leaking.

Fixes #182192

[flutter-dashboard]

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[gemini-code-assist]

Code Review

This pull request introduces a FlEGLImage GObject to manage the lifecycle of EGLImage handles, fixing a memory leak. The FlFramebuffer struct is updated to use this new GObject instead of a raw EGLImage handle. The related functions are modified to use GObject reference counting (g_object_ref, g_clear_object) for proper ownership and cleanup of the EGL image, especially when it is shared between sibling framebuffers.

[robert-ancell]

Updated as Gemini did a better review in #183653 :)

[mattkae]

Nice, checks out !