[X86][GlobalISel] Enable G_BUILD_VECTOR and G_CONSTANT_POOL (#92844)

* Add support for G_LOAD from G_CONSTANT_POOL on X86 and X64
* Add X86GlobalBaseRegPass to handle base register initialization for
X86.
* Fix vector type legalization for G_STORE and G_LOAD as well as enable
scalarization for them.
* Custom lower G_BUILD_VECTOR into G_LOAD from G_CONSTANT_POOL.