Debugger: Add support for hover variable values

[jpike88]

Summary

This is probably not strictly a bug, but it's such a crucial aspect of debugging that it might as well be.

When breakpointed, variable value summaries are not displayed in a tooltip. The types are great but it's not enough for effective debugging.

see existing functionality in vscode:

Zed Version and System Specs

Zed: v0.191.4 (Zed Preview)
OS: macOS 16.0.0
Memory: 32 GiB
Architecture: aarch64

[andreasvh-conceto]

from vim mode perspective it would be awesome to navigate over the variable and show the variables value per default via g h or shift-k. Pressing the buttons again would allow the user to navigate inside this object and its values via h j k l