[mlir][memref] Move AllocLikeConversion.h helpers into MemRefToLLVM.cpp (#136424)

This commit moves code around: The helper functions/classes are moved
into `MemRefToLLVM.cpp`. This simplifies the code a bit: fewer
templatized functions, fewer function calls, fewer lines of code.

This commit also moves checks in `matchAndRewrite` to the beginning of
the functions, such that patterns bail out (`return failure()`) before
starting to modify any IR. (Apart from that, this change is NFC.) This
is in preparation of the One-Shot Dialect Conversion refactoring, which
will disallow pattern rollbacks.

Author: matthias-springer

mlir/include/mlir/Conversion/MemRefToLLVM/AllocLikeConversion.h

@@ -1,5 +1,4 @@
 add_mlir_conversion_library(MLIRMemRefToLLVM
-  AllocLikeConversion.cpp
   MemRefToLLVM.cpp
 
   ADDITIONAL_HEADER_DIRS