[mlir][doc] Fix links and references in documentation of Dialects

This patch is the first in a series of patches fixing markdown links and references inside the mlir documentation. I chose to split it in a few reviews to be able to iterate quicker and to ease review.

This patch addresses all broken references to other markdown files and sections inside the Dialects folder.

One change that was also done was to insert '/' between the markdown files and section:
Example:
Builtin.md#integertype
was changed to:
Builtin.md/#integertype

After compilation, hugo then translates the later to jump directly to the integer type section, but not the former. Not inserting the slash would simply jump to just the Builtin page, instead of the integertype section. I therefore changed occurrences of the former version to the later as well.

Differential Revision: https://reviews.llvm.org/D103011