There were InstLoad::getSourceAddress() and InstStore::getAddr()
methods, which aren't very clear and consistently named. This change
replaces them with getLoadAddress() and getStoreAddress(), respectively.

This will also enable moving these methods to the Inst class to make
them available for SubVectorLoad and SubVectorStore intrinsics. While
these methods don't make sense for other instructions, note that
Inst::getSrc() already provides access to all operands and has to be
used with knowledge of the operand meaning and layout. So this only
provides a name to these operands, and it would stick out as a sore
thumb if used incorrectly.

Bug: b/179497998
Change-Id: I86b1201b8a1c611682f4f91541bdb49e17ef71a8
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52530
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>