[MC-61379] Extra tag in tellraw on signs has problems with tellraw as clickEvent

This relates to: ~~MC-59504~~ but is not a duplicate

It seems like the extra-tag in signs (and maybe books) is broken, or has problems with analysing commands (at least tellraw commands) in the clickEvent-tag:

Without extra-tag

/setblock ~ ~1 ~ standing_sign 5 replace {Text1:"{text:'CLICK',clickEvent:{action:run_command,value:'/tellraw @p {text:\"Hi\"}'}}"}

With extra-tag

/setblock ~ ~1 ~ standing_sign 5 replace {Text1:"{extra:[{text:'CLICK',clickEvent:{action:run_command,value:'/tellraw @p {text:\"Hi\"}'}}]}"}

This won't work