The current support was essentially the amount necessary
to support replacing SymbolRefAttrs, but suffers from various
deficiencies (both ergonomic and functional):
* Replace crashes if unsupported
This makes it really hard to use safely, given that you don't know
if you are going to crash or not when using it.
* Types aren't supported
This seems like a simple missed addition when the attribute replacement
support was originally added.
* The ergonomics are weird
It currently uses an index based replacement, which makes the implementations
quite clunky.
This commit refactors support to be a bit more ergonomic, and also
adds support for types in the process. This was also a great oppurtunity
to greatly simplify how replacement is done in the symbol table.
Fixes#56355
Differential Revision: https://reviews.llvm.org/D130589
01eedbc7c1