feat(bounded_continuous_function): coe_sum (#6522)
feat(bounded_continuous_function): coe_sum (#6522)




Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>
Co-authored-by: Rob Lewis <f89db59e6074667375662ee222555a187f42739f@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib