feat(screenshot): support out-of-proc capture

[mujacica]

Add a pid parameter to sentry__screenshot_capture() to allow capturing the windows of a specific process instead of always using the current process. Passing 0 preserves the existing behavior.

This is needed for the upcoming native backend (#1433), where a daemon process captures screenshots on behalf of the crashed application.

Partially cherry-picked from 62f1cdb (#1433)

#skip-changelog (internal)

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[jpnurmi]

Tested with a fake out-of-proc setup on Windows

diff --git a/src/backends/sentry_backend_inproc.c b/src/backends/sentry_backend_inproc.c
index 6efd2ad4..6b97fb8d 100644
--- a/src/backends/sentry_backend_inproc.c
+++ b/src/backends/sentry_backend_inproc.c
@@ -1169,7 +1169,7 @@ process_ucontext_deferred(const sentry_ucontext_t *uctx,
                 sentry_attachment_t *screenshot = sentry__attachment_from_path(
                     sentry__screenshot_get_path(options));
                 if (screenshot
-                    && sentry__screenshot_capture(screenshot->path, 0)) {
+                    && sentry__screenshot_capture(screenshot->path, 2988)) {
                     sentry__envelope_add_attachment(envelope, screenshot);
                 }
                 sentry__attachment_free(screenshot);