Only show images during tests when requested via project property (#2177)

## Description

Revision of #2164. Instead of only running headless tests during a
build, now only the images are disabled. To reenable showing images, the
`enableTestUi` project property needs to be passed to gradle.

```bash
./gradlew test -PenableTestUi
```

## Meta

Merge checklist:
- [X] Pull Request title is [short, imperative
summary](https://cbea.ms/git-commit/) of proposed changes
- [X] The description documents the _what_ and _why_
- [X] This PR has been
[linted](https://docs.photonvision.org/en/latest/docs/contributing/linting.html).
- [x] If this PR changes behavior or adds a feature, user documentation
is updated
- [ ] If this PR touches photon-serde, all messages have been
regenerated and hashes have not changed unexpectedly
- [ ] If this PR touches configuration, this is backwards compatible
with settings back to v2025.3.2
- [ ] If this PR touches pipeline settings or anything related to data
exchange, the frontend typing is updated
- [ ] If this PR addresses a bug, a regression test for it is added

shared/common.gradle

@@ -54,24 +54,14 @@ dependencies {
 
 test {
     useJUnitPlatform()
-    testLogging {
-        events "passed", "skipped", "failed", "standardOut", "standardError"
-    }
-    workingDir = new File("${rootDir}")
-    finalizedBy jacocoTestReport
-}
-
-tasks.register('testHeadless', Test) {
-    group = "verification"
-    systemProperty("java.awt.headless", "true")
-    useJUnitPlatform()
+    systemProperty("java.awt.headless", !project.hasProperty("enableTestUi"))
     testLogging {
         events "passed", "skipped", "failed", "standardOut", "standardError"
         exceptionFormat = "full"
         showStandardStreams = true
     }
-    exclude '**/*BenchmarkTest*'
     workingDir = new File("${rootDir}")
+    finalizedBy jacocoTestReport
 }
 
 jacoco {
@@ -80,7 +70,7 @@ jacoco {
 }
 
 jacocoTestReport {
-    dependsOn testHeadless
+    dependsOn test
 
     reports {
         xml.required = true
@@ -96,10 +86,3 @@ jacocoTestReport {
         }))
     }
 }
-
-// Only run headless tests from the build task
-gradle.taskGraph.whenReady { graph ->
-    if (graph.hasTask(build)) {
-        test.enabled = false
-    }
-}