Share the default VAO state between all frontend VAO when
there is no native VAO support. Forcefully sync state every
time a new frontend VAO is bound.

Bug: angleproject:5577, chromium:1167179
Change-Id: Ieaedb5108ad28fc78e7e58b74495639c5246bb05
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2665266Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>