use gdb's `-list-feature` instead of heuristics

**Is your feature request related to a problem? Please describe.**
gdb features, such as whether reverse debugging is enabled, is currently guessed at by gdbgui.

**Describe the solution you'd like**
use `-list-feature` instead of guessing gdb's features

https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Support-Commands.html#GDB_002fMI-Support-Commands

Start by locating gdbgui's existing heuristic checks for GDB features and read the linked GDB/MI Support Commands documentation for `-list-feature`. Done means feature detection, including reverse-debugging availability, uses the GDB response instead of guesses; there are no tests or file paths mentioned in the issue.

Written by the indexing model from the issue text.