Add declaration to session after modifying a default PROTO parameter

[stefaniapedrazzi]

Fixes #5026:

• [x] when modifying a PROTO parameter the PROTO declaration is added to the world EXTERNPROTO declarations
• [x] when displaying the PROTO URL (Add Node dialog and Node editor), use the node URL directly if the node is not found in the world declarations
• [x] remove declaration when resetting PROTO to default value

Tests:

• [x] open world with local PROTO not declared and select it
• [x] open world with a not declared PROTO node as default PROTO node parameter (not written in WBT file), and select it
• [x] modify default parameter, save world -> PROTO is added to the WBT file
• [x] reset default parameter, save world -> PROTO is removed from the WBT file
• [ ] use different URL in world and PROTO file for default parameter:
  • [ ] in case of default parameter -> PROTO declaration should be used
  • [ ] in case of modified parameter -> world declaration should be used
• [ ] ...

[stefaniapedrazzi]

Currently, if the world has a different EXTERNPROTO URL than the PROTO the behavior is correct but only after saving and reverting the world. However the conflicting message is printed in the console:

Conflicting declarations for '%1' are provided: %2 and %3, the first one will be used after saving and reverting the world.
To use the other instead you will need to change it manually in the world file."

[stefaniapedrazzi]

Test suite is broken on the master branch, this PR fixes one of the current assertion failure but not the other one (see #5059) I tested locally after commenting out the other assertion that fails and all the tests passed successfully.

[stefaniapedrazzi]

All the tests are now passing and this PR is ready for review.