internal/abi, runtime, cmd: merge PCDATA_* and FUNCDATA_* consts into internal/abi

internal/abi, runtime, cmd: merge PCDATA_* and FUNCDATA_* consts into internal/abi

We also rename the constants related to unsafe-points: currently, they
follow the same naming scheme as the PCDATA table indexes, but are not
PCDATA table indexes.

For #59670.

Change-Id: I06529fecfae535be5fe7d9ac56c886b9106c74fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/485497
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>