Long completion tooltips freezes the console for a while

Reproduce the issue with Register-ArgumentCompleter and menu completion via Ctrl+Space, using the long-tooltip example in the report. Trace the completion tooltip handling and verify that long tooltips are truncated, the console remains responsive, and the second completion can be selected without another freeze.

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues, especially the pinned issues.

Exception report

N/A

Screenshot

N/A

Environment data

PS Version: 7.5.0-preview.2
PS HostName: ConsoleHost
PSReadLine Version: 2.3.4
PSReadLine EditMode: Windows
OS: 10.0.19041.1 (WinBuild.160101.0800)
BufferWidth: 282
BufferHeight: 9001

Steps to reproduce

1. Register an argument completer where at least one of the completions has a really long tooltip
2. Trigger it with menu completion (Ctrl+Space)
3. Watch the console freeze and CPU usage rise as the long string is processed

Here's an example of this:

Register-ArgumentCompleter -CommandName Get-ChildItem -ParameterName Filter -ScriptBlock {
    [System.Management.Automation.CompletionResult]::new("CompletionText", "ListItem", [System.Management.Automation.CompletionResultType]::ParameterValue, "T$("o" * 1mb)ltip")
    [System.Management.Automation.CompletionResult]::new("OtherRes1", "OtherRes2", [System.Management.Automation.CompletionResultType]::ParameterValue, "OtherRes3")
}
Get-ChildItem -Filter <Ctrl+Space>

If you wait for it to fully load and move the cursor over to the second result and then back it will freeze again.

Obviously this is a silly example but PowerShell can generate really long tooltips in more realistic scenarios. For example if you parse a long script and hover over the scriptblock Ast the tooltip will contain the entire script, so if you've parsed a really big script you will see this freeze.

Expected behavior

No freezes and a truncated tooltip is visible.

Actual behavior

Freeze for several seconds and no tooltip.