spirv: Don't add decorations we ignore to the list

Certain decorations are not used by our code, so don't even bother
creating a vtn_decoration and adding them to the list.  This is
convenient since we don't need to include those (to ignore) in
different various switches.

SpvDecorationCounterBuffer and SpvDecorationUserSemantic, which can be
safely ignored by the driver, are now ignored only once.  This will
fix a missing handling of SpvDecorationCounterBuffer decoration (to
ignore it).
13 jobs for !1336 with r/spirv-ignore-decs in 13 minutes and 21 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #419308
debian

00:02:39

 
  Build+Test
passed #419317
meson-arm64

00:02:33

passed #419316
meson-armhf

00:01:56

passed #419310
meson-clang

00:10:41

passed #419314
meson-clover

00:09:20

passed #419318
meson-i386

00:01:44

passed #419313
meson-main

00:08:23

passed #419309
meson-swr-glvnd

00:08:21

passed #419315
meson-vulkan

00:03:50

passed #419320
scons-llvm

00:04:07

passed #419319
scons-nollvm

00:03:51

passed #419311
scons-swr

00:10:00

passed #419312
scons-win64

00:10:36