Preserve client console scroll position when trimming history

[HeresHavi]

Summary

Preserved the visible F8 console position when new output causes older history to be removed.

The console still follows new output while viewing the bottom, and trimming now handles wrapped and multibyte text correctly.

Motivation

The console keeps a limited amount of history. When that limit was reached, older lines were removed from the top while the previous scrollbar position was restored unchanged. This made the visible content jump forward even though the user had scrolled back to read earlier output.

For example, a developer may scroll up to inspect an earlier error while a busy resource continues printing messages. Once the history starts trimming, the console could move away from the lines they were reading.

Test plan

Runtime

• Before Fix: Filled the console with numbered lines, scrolled to a known position, and added timed output. The visible content moved when history trimming started.
• After Fix: Repeated the same test and confirmed the same retained text stayed visible.
• Valid Case: The console continued following new output normally while scrolled to the bottom.
• Wrapped Text: Repeated the test with heavily wrapped 300-character lines.
• Unicode: Tested buffer rollover with é and 界. The text stayed intact and the viewport did not move.
• Oldest Lines: Confirmed that when the currently viewed lines had to be removed, the console stayed at the top and showed the earliest retained complete line.

Builds and Tests

• Debug | Win32: Client tests built, 304 tests passed.
• Release | Win32: Full solution build passed, 304 client tests passed.
• Release | x64: Server build passed.
• Ran clang-format.

Checklist

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