perf(term): add benchmarks

Adds benchmarks by running [alacritty/vtebench](https://github.com/alacritty/vtebench)
benchmarks in the terminal.
Uses code based on [godotengine/godot-benchmarks](https://github.com/godotengine/godot-benchmarks)
to measure average GPU and CPU time spent per frame.
Uses [github-action-benchmark](https://github.com/benchmark-action/github-action-benchmark)
for continuous integration, and publishes benchmark results to https://lihop.github.io/godot-xterm/dev/bench/.

benchmark/results/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore