jvm_exclude with Group Only Fails Parsing by Coursier

[NGustafson]

Describe the bug
Running pants generate-lockfiles when a jvm_artifact contains a jvm_exclude that only specifies a group will fail with a "Failed to parse [group-name]" message from Coursier. This is contrary to the documentation for jvm_exclude which states "jvm_exclude: Exclude the given artifact and group, or all artifacts from the given group."

Pants version
2.20.0rc2

OS
MacOS

Additional info
Example Repo https://github.com/NGustafson/pants-examples/blob/main/3rdparty/jvm/BUILD
This repo has a single jvm_artifact with nothing else configured. Attempting to run pants generate-lockfiles will cause this error:

pants generate-lockfiles
[ERROR] 1 Exception encountered:

Engine traceback:
  in `generate-lockfiles` goal

ProcessExecutionFailure: Process 'Running `coursier fetch` against 1 requirement: org.slf4j:slf4j-log4j12:2.0.12' failed with exit code 1.
stdout:

stderr:
+ coursier_exe=__coursier/./cs-aarch64-apple-darwin
+ shift
+ json_output_file=coursier_report.json
+ shift
++ pwd
+ working_dir=/private/var/folders/cm/gmrdwxcn7tv_cct4dzg38w91kjyl1q/T/pants-sandbox-aM4FVB
+ __coursier/./cs-aarch64-apple-darwin fetch -r=https://maven-central.storage-download.googleapis.com/maven2 -r=https://repo1.maven.org/maven2 --no-default --json-output-file=coursier_report.json org.slf4j:slf4j-log4j12:2.0.12 --local-exclude-file PANTS_RESOLVE_EXCLUDES
Failed to parse org.slf4j
Failed to parse org.slf4j

[huonw]

Thanks for filing an issue with a reproducer and sorry for the trouble!

I did an initial triage to check priority/regression: it looks like this behaviour has existed since 2.18.0.dev0 (PANTS_VERSION=2.18.0.dev0 pants generate-lockfiles), which seems to be the first release that had this jvm_exclude #19128, so not a regression.

@NGustafson is this something you might have a chance at trying to fix? @alonsodomin is something you can provide hints or guidance about?

[NGustafson]

@huonw Thanks for checking! Yes I'd like to try fixing this.
It seems like Coursier supports group-only excludes if you set the artifact to *. Something like --exclude 'org.slf4j:*'. But this Pants syntax causes a different error jvm_exclude(group="org.slf4j", artifact="*"), so I'm going to try getting that to work first.

[alonsodomin]

sorry for the trouble, it's true that initial implementation was wrong. This should be easy to fix, the point in which the exclusion is transformed into a coordinate string is in here:

pants/src/python/pants/jvm/target_types.py

Line 308 in b7b0e9c

def to_coord_str(self) -> str: