Refactor InstKind to move metadata from macros to the type.

[jonmeow]

This adds DefinitionInfo for Define-based configuration so that parameters are optional. It also makes it easier to provide the equivalent functions on both Definition and Define.

A common pattern used here is to change from a switch with in-line cases to instead have cases that call an overloaded function. What's happening here is that the instruction type is used to select an overload, and if an overload is not defined, a compiler error would result. Meanwhile, clusters of overloads are being defined using requires-based templating, so that equivalent implementations are not copied. This addresses a limitation of a vanilla switch approach where it's hard to have redundant cases using conditional logic, while also getting compiler errors when adding new InstKind entries, which had been a significant part of why we used macros previously.

This starts hitting some odd clang-format edge cases causing CARBON_KIND_SWITCH(inst){ (missing space), which I haven't seen before. Adding CARBON_KIND_SWITCH to .clang-format works around it.