Auto upgrade SVG and text annotations to annotation layer items on project load

[nyalldawson]

When loading old projects, any of the old SVG and text annotations will automatically be converted to the newer picture and rectangular text annotation item types.

Remove the actions for creating new SVG and text annotations, and require users to use the corresponding annotation items instead.

Refs qgis/QGIS-Enhancement-Proposals#269

[github-actions]

🪟 Windows builds ready!

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(Built from commit ff96802)

[qgis-bot]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@nyalldawson

This pull request has been tagged for the changelog.

• The description will be harvested so please provide a "nearly-ready" text for the final changelog
• If possible, add a nice illustration of the feature. Only the first one in the description will be harvested (GIF accepted as well)
• If you can, it's better to give credits to your sponsor, see below for different formats.

You can edit the description.

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Thank you!

[nirvn]

Nice work.

[qgis-bot]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#9211
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!