Aggregate junit report into one file (#1056)

Some systems require junit report to be in a single file. For example `bazel` https://bazel.build/reference/test-encyclopedia needs single file to be available in `XML_OUTPUT_FILE` path.

To avoid implementing junit aggregation in pkl wrappers in different places this PR instead adds a `--junit-aggregate-reports` flag to return all junit reports as a single file.

Additional flag `--junit-aggregate-suite-name` is added to allow overriding global test suite name from default `pkl-tests`

docs/modules/pkl-cli/pages/index.adoc

@@ -465,9 +465,31 @@ Default: (none) +
 Example: `./build/test-results` +
 Directory where to store JUnit reports.
 
+By default, one file will be created for each test module. This behavior can be changed with `--junit-aggregate-reports`, which will instead create a single JUnit report file with all test results.
+
 No JUnit reports will be generated if this option is not present.
 ====
 
+[[junit-aggregate-reports]]
+.--junit-aggregate-reports
+[%collapsible]
+====
+Aggregate JUnit reports into a single file.
+
+By default it will be `pkl-tests.xml` but you can override it using `--junit-aggregate-suite-name` flag.
+====
+
+[[junit-aggregate-suite-name]]
+.--junit-aggregate-suite-name
+[%collapsible]
+====
+Default: (none) +
+Example: `my-tests` +
+The name of the root JUnit test suite.
+
+Used in combination with `--junit-aggregate-reports` flag.
+====
+
 [[overwrite]]
 .--overwrite
 [%collapsible]
@@ -555,6 +577,26 @@ Directory where to store JUnit reports.
 No JUnit reports will be generated if this option is not present.
 ====
 
+[[junit-aggregate-reports]]
+.--junit-aggregate-reports
+[%collapsible]
+====
+Aggregate JUnit reports into a single file.
+
+By default it will be `pkl-tests.xml` but you can override it using `--junit-aggregate-suite-name` flag.
+====
+
+[[junit-aggregate-suite-name]]
+.--junit-aggregate-suite-name
+[%collapsible]
+====
+Default: (none) +
+Example: `my-tests` +
+The name of the root JUnit test suite.
+
+Used in combination with `--junit-aggregate-reports` flag.
+====
+
 .--overwrite
 [%collapsible]
 ====

docs/modules/pkl-gradle/pages/index.adoc

@@ -195,7 +195,7 @@ Example 1: `multipleFileOutputDir = layout.projectDirectory.dir("output")` +
 Example 2: `+multipleFileOutputDir = layout.projectDirectory.file("%{moduleDir}/output")+`
 The directory where a module's output files are placed.
 
-Setting this option causes Pkl to evaluate a module's `output.files` property 
+Setting this option causes Pkl to evaluate a module's `output.files` property
 and write the files specified therein.
 Within `output.files`, a key determines a file's path relative to `multipleFileOutputDir`,
 and a value determines the file's contents.
@@ -207,7 +207,7 @@ This option cannot be used together with any of the following:
 
 This option supports the same placeholders as xref:output-file[outputFile].
 
-For additional details, see xref:language-reference:index.adoc#multiple-file-output[Multiple File Output] 
+For additional details, see xref:language-reference:index.adoc#multiple-file-output[Multiple File Output]
 in the language reference.
 ====
 
@@ -298,6 +298,22 @@ Example: `junitReportsDir = layout.buildDirectory.dir("reports")` +
 Whether and where to generate JUnit XML reports.
 ====
 
+[[junit-aggregate-reports]]
+.junitAggregateReports: Property<Boolean>
+[%collapsible]
+====
+Default: `false` +
+Aggregate JUnit reports into a single file.
+====
+
+[[junit-aggregate-suite-name]]
+.junitAggregateSuiteName: Property<String>
+[%collapsible]
+====
+Default: `null` +
+The name of the root JUnit test suite.
+====
+
 [[overwrite]]
 .overwrite: Property<Boolean>
 [%collapsible]
@@ -391,7 +407,7 @@ For Spring Boot applications, and for users of `pkl-config-java` compiling the g
 Default: `"org.pkl.config.java.mapper.NonNull"` +
 Example: `nonNullAnnotation = "org.project.MyAnnotation"` +
 Fully qualified name of the annotation type to use for annotating non-null types. +
-The specified annotation type must be annotated with `@java.lang.annotation.Target(ElementType.TYPE_USE)` 
+The specified annotation type must be annotated with `@java.lang.annotation.Target(ElementType.TYPE_USE)`
 or the generated code may not compile.
 ====
 
@@ -431,7 +447,7 @@ build.gradle.kts::
 +
 [source,kotlin]
 ----
-pkl { 
+pkl {
   kotlinCodeGenerators {
     register("genKotlin") {
       sourceModules.addAll(files("Template1.pkl", "Template2.pkl"))