fix(bash): Restore previous exit status in bash init

[chipbuster]

Description

Restore the previous exit status so that any subsequent hooks in the PROMPT_COMMAND pipeline can run with the correct return code.

Motivation and Context

Closes #2918

Screenshots (if appropriate):

How Has This Been Tested?

I've confirmed that this doesn't negatively affect bash init, but I haven't confirmed that this actually causes the behavior intended. The fix is based on a comment by lilyball on the linked issue.

Checklist:

• I have updated the documentation accordingly.
• I have updated the tests accordingly.

[chipbuster]

I can't request changes on my on my own PR, but I can merge it without an approving review? What??

Anyways, some testing has revealed that this does not entirely solve the linked issue, so let's not merge this until I've had a chance to test it more thoroughly.

[andytom]

Blocking for now

[andytom]

I can't request changes on my on my own PR, but I can merge it without an approving review? What??

Anyways, some testing has revealed that this does not entirely solve the linked issue, so let's not merge this until I've had a chance to test it more thoroughly.

Ooo interesting what are the problems it seemed to work fine for me locally, I only did a wee bit of testing so maybe I missed something.

[chipbuster]

Here's what I used to test, starting up from a shell with (almost) no config:

derp(){ echo "Previous exit was $?"; }
PROMPT_COMMAND=derp

# Separate commands, should result in exit codes of 0, 1, and 127
true
false
doesnotexist

eval "$(starship init bash)"

true
false
doesnotexist

With the previous version, after starship init bash, on my system, I would always get "Previous exit was 0".

Shell version is GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu)

[chipbuster]

Okay, I think this fixes the problem I saw.