Color curly brackets based on role

[zopsicle]

Currently, curly brackets are always colored purple. It would be convenient if they were colored according to the role of the block, like identifiers are.

a←{@}    # subject role; white curly brackets
B←{𝕩}    # function role; green curly brackets
_c←{𝔽}   # 1-modifier role; orchid curly brackets
_d_←{𝔾}  # 2-modifier role; orange curly brackets

I don’t know the exact rules for deducing the role, but there are some non-trivial cases so this might not be very easy to implement in a CodeMirror language, such as:

{'a'}{𝔽}↕10
#    #
#    # 1-modifier role
#
# function role