Add outputEncoding parameter to enable encoding conversion (MRESOURCES-232)

[gnodet]

Summary

Adds a new outputEncoding plugin parameter that configures the character encoding used to write filtered resources. When set, the plugin reads source files with encoding and writes filtered output with outputEncoding, enabling lossless encoding conversion during the build.

Closes #335

Companion filtering PR: apache/maven-filtering#407

Use case

Converting a legacy EBCDIC or Latin-1 (ISO-8859-1) source tree to UTF-8 output without manually converting the source files:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-resources-plugin</artifactId>
  <configuration>
    <encoding>ISO-8859-1</encoding>
    <outputEncoding>UTF-8</outputEncoding>
  </configuration>
</plugin>

Or as a CLI property: -Dmaven.resources.outputEncoding=UTF-8

Per-resource encoding override via <encoding> / <outputEncoding> inside a <resource> block is also supported (requires the companion filtering PR to be released first).

Notes

• The parameter only applies to filtered resources (<filtering>true</filtering>). Non-filtered files are always copied as raw bytes — encoding is irrelevant for them.
• When outputEncoding is not set (the default), the same encoding is used for reading and writing, preserving full backward compatibility.
• pom.xml references maven-filtering 4.0.0-beta-2-SNAPSHOT for local build; will be updated to the released version once the companion PR is merged and released.

Changes

• ResourcesMojo: new @Parameter outputEncoding field wired into MavenResourcesExecution.setOutputEncoding()
• src/it/MRESOURCES-232/: IT with a Latin-1 source file containing a filter token and an é character; verifies the output file is UTF-8-encoded with the token expanded and é surviving as 0xC3 0xA9

Closes #335

[gnodet-bot]

Clean feature addition — well-structured parameter, good Javadoc, solid IT with both string and byte-level verification. One inaccuracy to fix on the @since tag.

The SNAPSHOT dependency on maven-filtering 4.0.0-beta-2-SNAPSHOT is acknowledged in the PR description and expected to be updated before merge.

This review was generated by an AI agent, Hermès on behalf of @gnodet.

[gnodet-bot]

⚠️ Inaccurate @since tag — version 3.4.1 was never released (releases went 3.4.0 → 3.5.0 → 3.5.1). Since this PR targets master (the 4.x line), this should be:

Suggested change

	* @since 3.4.1
	* @since 4.0.0-beta-2

If backporting to the 3.x line as well, use the future 3.x release version there.