Make 'Instrument Text' available from ADD main menu

I am creating this issue at the request of Jojo Schmitz. The original discussion thread of this issue is at https://musescore.org/en/node/103861

Currently adding text to a score can be done three ways: via keyboard shortcut, via the ADD>Text... main menu, or via the F9 Palette 'Text' subpalette. However, ONLY from the F9 Text subpalette does the user have access to the 'Instrument Text' feature, which is required if one wishes to change an instrument in mid-staff. Users who habitually add anchored text to a score via keyboard shortcut or the ADD main menu may not realise that the third method, via the F9 palette, exists, or that it offers additional options.

Understanding that automtic transposition for 'transposing' instruments such as horns, trumpets, clarinets, saxes, and English horns is not presently supported, it would still be useful for the 'instrument text' option to appear in the drop-down from ADD>Text..., and creating a dedicated shortcut to enable that type of text would also be useful.

Additionally, it would be useful for the current, limited 'mid-staff instrument change' function to affect the short-name for the staff text for the staves within the selected matter, although that may be problematic given that the beginning/end of a new system may not coincide with the beginning/end of the 'doubled' instrument selection. My suggestion would be for the short-name to change on the next new system, and remain changed until after the end of the last system within which the changed instrument applies.

If that is not practical, the user will simply have to set the staff instrument name/short-name to include both instruments that the player will have to double.