SourceInfo: simplify the common case for makeMessage, print it differently

[mwachs5]

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• API modification

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference).

Release Notes

Add a default to SourceInfo.makeMessage() so that users don't always have to write makeMessage(x => x). Change the toString of SourceLine so that it puts a colon instead of a space between the file name and line number, which makes it possible to click-to-source in editors like VSCode.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[sequencer]

LGTM

[jackkoenig]

LGTM!

You have some failing tests though, they look like tests that just need to be updated for the new format:

[info] *** 4 TESTS FAILED ***
[error] Failed tests:
[error] 	chiselTests.experimental.hierarchy.InstantiateSpec
[error] 	chiselTests.WhenSpec
[error] 	chiselTests.simulator.SimulatorSpec

[dtzSiFive]

LGTM