[Feature]: assist with platform-specific classifiers on plugins

[ascopes]

Binary plugins will almost always have OS and CPU specific builds per target platform. The name of the target OS and platform are usually encoded in the binary name or the Maven classifier.

This can be problematic for users to ensure their builds remain cross-platform-compatible, since the scheme used to name the OS and CPU are not standardised and can have wildly different representations. For example:

• Do they call AMD64 processors "amd64", "x86_64", "x86-64", "x64", or use the 32 bit monikers such as "x86", "x86_32", "i386", "i486", "i586", "i686", etc?
• Do they call ARM processors "arm64", "aarch64", etc?
• Do they call Linux "linux", "unix", "posix", etc?
• Is macOS named "mac", "macos", "macintosh", "osx", "macos"
• Is Windows named "windows", "win", "win32", "win64", "w64", etc?
• Are these case sensitive?

The proposal is to add a configuration block to plugins that allows a user to supply a custom mapping of conditions to "template" a URL or Maven artifact based upon the platform or any other Maven properties that are defined.

This could take many forms, but one example could be:

<binaryMavenPlugin>
  <groupId>org.example</groupId>
  <artifactId>protobuf-gen-example-java</artifactId>
  <version>1.2.3</version>
  <classifier>#{os}</classifier>

  <templateMappings>
    <templateMapping>
      <os>
        <value>${os.name}</value>
        <replacements>
          <replacement>
            <match>/win(32|64|dows)/i</match>
            <replace>Win_32</replace>
          </replacement>
          <replacement>
            <match>/(linux|mac.*)/</match>
            <replace>$1</replace>
          </replacement>
        </replacements>
      </os>
    </templateMapping>
  </templateMappings>
</binaryMavenPlugin>

Other alternatives include:

• The user hardcodes the properties for classifiers based on Maven profile activations.
• The user pulls in a plugin such as gmavenplus to break out to an inline groovy script to make the decision on which properties to set.

[ascopes]

Moved to GH-676.