feat: partial attribute completion

[luckasRanarison]

Currently attribute completion only works when being at the beginning of an attribute list or after a comma and need to be triggered manually after inserting [ or after , . Being able to autocomplete attribute when starting to type the attribute name itself would be really convinnient.
For example, the following case doesn't get autocomplete:

digraph {
  start -> end [sha|]
                // ^ cursor here
}

This is an attempt to solve that problem but I'm stuck on the above case, the current node is TextIdentifier and the previous node kind type is AttributeContainer but this is also the case in the following situation (#17):

digraph {
  start -> end [color=blue]
  s|
// ^ cursor here
}

So we don't have enough context... I'd be happy to hear your thoughts on this.

[nikeee]

I added some CI and formatting checks to master and updated this branch.