backtraces are hard to read

[heycam]

I find Rust backtraces hard to read at a glance. I think it's because many irrelevant (to me) stack frames are shown -- I'm getting 11 frames at the top relating to panicking and backtrace printing, and at the bottom there are 8 relating to panic catching and other initialization. The frames I really want to look at are somewhere in the middle, but I have trouble scanning the output to find them.

Two potential ideas for improving the readability:

1. Omit the panic / backtrace / initialization frames by default, and only show them when RUST_BACKTRACE=full is used.
2. Color code the output so that the panic / backtrace / initialization frames are de-emphasized.

[jonas-schievink]

Duplicate of #58554