[22850] Fix python code generation for bounded strings (backport #440)

[mergify]

Description

This PR introduces the following improvements on the code generated for SWIG interfaces:

1. A setter for fixed_string members receiving a standard string is added.
2. A %template for each fixed_string member is generated.

This allows setting bounded string members with either of the following alternatives:

1. struct_name.member_name("string value")

2. fixed_str = fixed_string_16("string value")
   struct_name.member_name(fixed_str)
   

@Mergifyio backport 4.0.x

Contributor Checklist

• Commit messages follow the project guidelines.

• 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

  • See [22851] Add support for bounded strings Fast-DDS-python#209 for the added tests

• N/A: New feature has been documented/Current behavior is correctly described in the documentation.

• 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: failing tests are unrelated with the changes.

---

This is an automatic backport of pull request #440 done by [Mergify](https://mergify.com).

[mergify]

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	both modified:   src/main/java/com/eprosima/fastcdr/idl/templates/TypesSwigInterface.stg

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