[symbols-view] Remap go-to-declaration commands on Windows/Linux

[savetheclocktower]

This is a quick one. @Spiker985 discovered that the Symbols View: Go To Declaration and Symbols View: Return From Declaration commands used key shortcuts that shadowed the built-in Editor: Add Selection Above and Editor: Add Selection Below commands on Windows and Linux.

The symbols-view commands didn't even have mapped keys on Windows until 1.113. (If I had to guess, I'd guess that ctags didn't work on Windows at some point?) But these commands have always conflicted with one another on Linux!

To fix this, I'm adding a modifier key to the default key combinations on these two platforms. These new key combinations don't conflict with anything in the core keymaps folder, nor any other keymaps I can find in the pulsar project.

[DeeDeeG]

I've tested this just now. I'm pretty sure this is a desirable outcome from the tests?

On Windows:

• Pulsar 1.113.0 (without this PR)
  • Ctrl + Alt + Down flips my display output upside-down ❌
  • Ctrl + Shift + Alt + Down does nothing ❌
• Pulsar bins from this PR (Pulsar "1.113.2024021522")
  • Ctrl + Alt + Down still flips my display output upside-down ❌
  • Ctrl + Shift + Alt + Down goes to the definition of the thing my cursor is on ✅ <-- this is what we want

Tested with https://web.pulsar-edit.dev/packages/pulsar-ide-clangd and clangd in a .c file.

[DeeDeeG]

Merging now, thanks!