Results 10 issues of Alexander Pavlov

Resolves: *https://github.com/musescore/MuseScore/issues/8601* *Fixed the following bugs:* - Not possible to change cross notehead after opening gp file - Parenthesis instead of cross in tab notation - [x] I signed [CLA](https://musescore.org/en/cla)...

Resolves: *(direct link to the issue)* *(short description of the changes and the motivation to make the changes)* - [ ] I signed [CLA](https://musescore.org/en/cla) - [ ] I made sure...

Resolves: *(direct link to the issue)* *(short description of the changes and the motivation to make the changes)* - [ ] I signed [CLA](https://musescore.org/en/cla) - [ ] I made sure...

fixed creation of KeySig and treated situation when segment is nullptr

fixed behaviour when guitar pro file contains random octava signs on rests (bug of guitar pro)

fixed position of palm mute below/above the staff (pay attention to simple tab staff type) Current behaviour: ![Screenshot 2023-01-16 at 16 07 52](https://user-images.githubusercontent.com/24373905/212697193-6a46e862-9c5a-4075-a34d-9d2e4f401667.png) Expected: ![Screenshot 2023-01-16 at 16 08 13](https://user-images.githubusercontent.com/24373905/212697250-40b508df-e940-4f66-a4c3-1cf59a8d79d6.png)

Current behaviour: ![Screenshot 2023-01-15 at 20 14 38](https://user-images.githubusercontent.com/24373905/212559262-d5222128-dc42-4d51-a0cf-07718ebecee8.png) Expected: ![Screenshot 2023-01-15 at 20 15 32](https://user-images.githubusercontent.com/24373905/212559305-55337e0b-af7c-4e57-a543-8247aa139f27.png) [octave-regression.gp.zip](https://github.com/musescore/xtz/files/10420885/octave-regression.gp.zip)

Current behaviour: ![Screenshot 2023-01-16 at 23 02 44](https://user-images.githubusercontent.com/24373905/212765238-274c155e-4e8f-4745-a786-87339dba6cdd.png) Expected: ![Screenshot 2023-01-16 at 23 03 00](https://user-images.githubusercontent.com/24373905/212765271-c76dd1a5-e23d-419f-bd28-ff856c7b3ced.png)