Introduce BugChecker for implicit var usage

[dskop]

This PR introduces an error-prone pattern to check for implicit var keyword usage.
Examples:

var a = getList(); // should be flagged

var a = "string literal"; // should NOT be flagged because the expression includes literal
var a = (List) getList(); // should NOT be flagged because the expression includes type cast
var a = new Object(); // should NOT be flagged because the expression includes `new` operation
var a = getForType(List.class); // should NOT be flagged because the expression includes .class literal
var a = getList().map(String::new).findAny(); // should NOT be flagged because the expression includes constructor reference
var a = ImmutableList.of(42) // should NOT be flagged because the expression includes static constructor method

[github-actions]

• Surviving mutants in this change: 7
• Killed mutants in this change: 23

class	surviving	killed
🧟tech.picnic.errorprone.bugpatterns.ImplicitVarUsage	7	23

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

• Arcmutate licence valid until 2025-10-27 (yyyy/mm/dd) (non-commercial use only)
• Project uses Spring, but the Arcmutate Spring plugin is not present.
• TestNG is on the classpath but the pitest TestNG plugin is not installed.

[rickie]

Nice work @dskop, by running ./apply-error-prone-suggestions.sh we can resolve most of the errors that are pointed out!

Make sure to read the README on how to make sure you can run that :). If you're stuck with it, feel free to DM me on Slack.

[github-actions]

• Surviving mutants in this change: 7
• Killed mutants in this change: 23

class	surviving	killed
🧟tech.picnic.errorprone.bugpatterns.ImplicitVarUsage	7	23

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

• Arcmutate licence valid until 2025-10-27 (yyyy/mm/dd) (non-commercial use only)
• Project uses Spring, but the Arcmutate Spring plugin is not present.
• TestNG is on the classpath but the pitest TestNG plugin is not installed.

[github-actions]

• Surviving mutants in this change: 7
• Killed mutants in this change: 23

class	surviving	killed
🧟tech.picnic.errorprone.bugpatterns.ImplicitVarUsage	7	23

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

• Arcmutate licence valid until 2025-10-27 (yyyy/mm/dd) (non-commercial use only)
• Project uses Spring, but the Arcmutate Spring plugin is not present.
• TestNG is on the classpath but the pitest TestNG plugin is not installed.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
85.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

• Surviving mutants in this change: 12
• Killed mutants in this change: 30

class	surviving	killed
🧟tech.picnic.errorprone.bugpatterns.ImplicitVarUsage	12	30

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

• Arcmutate licence valid until 2025-10-27 (yyyy/mm/dd) (non-commercial use only)
• Project uses Spring, but the Arcmutate Spring plugin is not present.
• TestNG is on the classpath but the pitest TestNG plugin is not installed.

[rickie]

/integration-test