XCDRv1: support extra bytes in optional types (backport #285)

[mergify]

Description

Some XCDRv1 implementations add extra bytes, usually alignment bytes, at the end of the serialized base type of an optional type. And this extra bytes are took into account in the parameter's length which describes the optional. Currently fastcdr doesn't support this. The parameter's length of a optional has to have the exact length of the serialized base type.

This PR introduces this flexibility to support other XCDRv1 implementations.

@Mergifyio backport 2.2.x

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• Any new/modified methods have been properly documented using Doxygen.
• Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: CI pass and failing tests are unrelated with the changes.

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This is an automatic backport of pull request #285 done by [Mergify](https://mergify.com).