perf(packages/codegen): remove `last` param from `writeWithMapNamed` (#25983)

Optimization to sourcemap and no-sourcemap builds.

`writeWithMapNamed` now always receives an `Identifier`, so all call sites pass `last` as `CAT_IDENT`. Remove the param and just write `state.last = CAT_IDENT` directly. This avoids using a register to pass a value which is always the same, and makes setting `last` cheaper too.

Add a new `writeIdent` function which `writeWithMapNamed` is converted to in no-sourcemap builds, which also doesn't have a `last` param.