Allow creation of antisense chains in sequence mode

[ljubica-milovic]

Background

This ticket covers the creation of antisense chains in sequence mode.
Layout/representation of antisense chains in sequence mode is covered in the following ticket: #5942.

Requirements

1. When appropriate monomers are selected right-clicking on the monomers should give a drop-down menu with the options of "Create RNA Antisense Strand" and "Create DNA Antisense Strand".

Appropriate selection described in ticket #5678.

1.1. When appropriate monomers are selected the "Create Antisense Strand" (issue: #5999) tool should be enabled.

1.2. If the selection of monomers in not appropriate the option in the drop-down menu, as well as the tool should be disabled.

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2.1. When "Create RNA/DNA Antisense Strand" is chosen from the drop-down menu or the "Create Antisense Strand" tool is used, the logic for creating the antisense chain in the same as for other modes, and already described in #5678 (requirements 2) for RNA and in #6383 for DNA.

2.2. Antisense and sense chains should be layouted following the logic described in #5942 (requirements 2 & 3).

2.3. If no other double-stranded sequences existed on the canvas before the creation of the new antisense chain, the sync icon should appear on the top bar and be enabled/toggled on by default #6254 (requirement 4).

UX