[dawn][native] Cleanup BGL creation to better support arraySize

Support for arraySize needs to update ExtractAndExpandBglEntries in
awkward ways because that method and other related code had accumulated
debt. Refactor it a bit in preparation for arraySize.

 - Separate the binding counts used to iterate the BGL from the ones
   used for the validation of total binding counts in the pipeline
   layouts. Extra bindings are accounted for in BindingCounts for
   currently unused ExternalTexture reserved resources (one sampler and
   two sampled textures) and the confusion could cause subtle bugs in
   the future.
 - Change ExtractAndExpandBglEntries to do the conversion to BindingInfo
   internally, which avoids the need to store a linked list of
   BindGroupLayoutEntry on the side. Rename it to
   ConvertAndExpandBGLEntries.
 - Make it return all of its results by value instead of a mix with
   pointers (also go down from 6 things returned to only 2).
 - Update SortBindingsCompare to work with BindingInfo and simplify the
   logic to only what is needed to get the invariants that BGL requires.
 - Make the various *BindingLayout aggregate types by removing their
   constructors and using a static ::From member function instead.
 - Move operator == and != to BindingInfo instead of having it defined
   in BindGroupLayoutInternal.h
 - Remove / inline a couple unused BindGroupLayoutInternal member
   functions.

Bug: 393558555
Change-Id: Idc5365b61460a51ed30d6e829b37dcb05ebd76e5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/236415
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>