Introduce `EagerStringFormatting` check

[Stephan202]

:exclamation: This PR is on top of #1138. :exclamation:

This is a draft PR; a bit more work (especially around tests) is required. I'm opening the PR already, as I'd like to reference it.

Suggested commit message:

Introduce `EagerStringFormatting` check (#1139)

This new check flag code that can be simplified and/or optimized by
deferring certain string formatting operations.

[sonarcloud[bot]]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
89.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions[bot]]

• Surviving mutants in this change: 20
• Killed mutants in this change: 69

class	surviving	killed
:zombie:tech.picnic.errorprone.bugpatterns.EagerStringFormatting$StringFormatExpression	13	26
:zombie:tech.picnic.errorprone.bugpatterns.EagerStringFormatting	7	43

Mutation testing report by Pitest. Review any surviving mutants by inspecting the line comments under Files changed.