Call Stack bounces when short-lived second requests start/stop

Issue Type: <b>Bug</b> When using the PHP debugger I have a request paused and awaiting, however while that request is running other requests are also running but not pausing, as expected. The problem is that while there is only one request in the call stack, the call stack for the paused request is expanded, however when a second request is running the paused call stack gets collapsed and it shows two requests, with the paused request having an expansion arrow. Then the second request ends and the call stack again shows the full single request's call stack. Because of the nature of the application and my local dev environment, this is constantly happening, and focusing on anything or expanding it doesn't prevent me form losing my place. VS Code version: Code 1.55.2 (3c4e3df9e89829dce27b7b5c24508306b151f30d, 2021-04-13T09:35:57.887Z) OS version: Windows_NT x64 10.0.19041 <details> <summary>System Info</summary> |Item|Value| |---|---| |CPUs|Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz (8 x 2592)| |GPU Status|2d_canvas: enabled<br>gpu_compositing: enabled<br>multiple_raster_threads: enabled_on<br>oop_rasterization: enabled<br>opengl: enabled_on<br>protected_video_decode: unavailable_off<br>rasterization: enabled<br>skia_renderer: enabled_on<br>video_decode: enabled<br>vulkan: disabled_off<br>webgl: enabled<br>webgl2: enabled| |Load (avg)|undefined| |Memory (System)|15.96GB (3.41GB free)| |Process Argv|--crash-reporter-id 7d9cd352-3b0d-45b8-a763-88770b5a2e02| |Screen Reader|no| |VM|0%| </details><details><summary>Extensions (47)</summary> Extension|Author (truncated)|Version ---|---|--- vscode-base64|ada|0.1.0 Bookmarks|ale|13.0.4 project-manager|ale|12.1.0 vscode-intelephense-client|bme|1.7.0 npm-intellisense|chr|1.3.1 bracket-pair-colorizer|Coe|1.0.61 dakara-foldplus|dak|1.5.1 hex-to-rgba|dak|1.0.0 php-class-generator-composer-psr-4|dam|1.0.1 vscode-eslint|dba|2.1.20 gitlens|eam|11.4.1 EditorConfig|Edi|0.16.4 vscode-npm-script|eg2|0.3.21 phpunit|ema|4.1.1 prettier-vs…