Add dictionary array support for current kernels

[viirya]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
This is used to track tasks of adding dictionary array support for current compute kernels.

Describe the solution you'd like

Add dictionary array support compute kernels:

• substring: Add dictionary array support for substring function #1656
• length: Add DictionaryArray support for length kernel #1672
• bit_length: Add DictionaryArray support for bit_length kernel #1673
• add: Support DictionaryArray in add kernel #1950
• subtract: Support DictionaryArray in subtract kernel #1970
• multiply: Support DictionaryArray in multiply kernel #1972
• divide: Support DictionaryArray in divide kernel #1982
• like: Support DictionaryArray in Like Kernels #1975
• unary: Support DictionaryArray in unary kernel #1989
• add_scalar: Support DictionaryArray in add_scalar kernel #2017
• subtract_scalar, multiply_scalar, divide_scalar: Add DataType::Dictionary support to subtract_scalar, multiply_scalar, divide_scalar #2019

More to come...

[tustvold]

Is this complete?

[viirya]

I think it is not yet. I will look for if any kernels need dictionary support. If no, I will close this then.

[viirya]

I think this can be closed now. All above kernels I thought of are supported with Dictionary now. If I miss any kernels, we can open new issues for them.