[DSLX:LS] Ansi color codes don't render in vscode problems pane

[cdleary]

Describe the bug
The dslx_ls produces ANSI escapes in the problems pane in VSCode.

To Reproduce
Install DSLX vscode extension
Point at dslx_ls installation
Make a type error where we're displaying member type diffs (e.g. a component within a tuple)
Observe the unredered ANSI escapes

Expected behavior
I think somehow other languages provide color coding? But if not we probably need to plumb a "can do ANSI escapes" from the outside world to the error rendering.

Screenshots

[hzeller]

I guess things to figure out

• Inside the error emitting code we should ask isatty(STDERR_FILENO) before proceeding to emit ANSI codes
• Why does VSCode terminal not understand ANSI codes ? I know for the terminal app inside VSCode they do understand these (even images, if enabled), so not supporting it in log output is kinda meh - maybe there is a plugin for that ?

[cdleary]

We do strip ANSI escapes when it's not a tty https://sourcegraph.com/github.com/google/xls@49cff5c1c03aad0e93f0459917b3f3268afb98ec/-/blob/xls/dslx/error_printer.cc?L83-85