Refactor blockRendering.Types to have type guards

[BeksOmega]

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Description

Currently the Types object has a bunch of methods like isField, isIcon, isInput, etc, which all return numbers, which are then used as predicates.

We should change these to be type guards so that we can elliminate explicit casts within the rendering code. E.g: https://github.com/BeksOmega/blockly/blob/4cd3e0466003dcc15b2cd6355354fed3575031b9/core/renderers/common/drawer.ts#L287

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[AshwanthramKL]

Hey @BeksOmega, can I work on this?

[BeksOmega]

@maribethb