Addressed code review feedback:
- Fixed some issues in the unit test
- Adjusted line wrapping in the docs
- Clarified comments in the bytecode reader

Adds a check that the bytecode buffer is aligned to any section
alignment requirements. Without this check, if the source buffer is not
sufficiently aligned, we may return early when aligning the data
pointer. In that case, we may end up trying to read successive sections
from an incorrect offset, giving the appearance of invalid bytecode.

This requirement is documented in the bytecode unit tests, but is not
otherwise documented in the code or bytecode reference.

This reverts commit c075fb8c37856365fb76d986ad3aefa2400b3240. This
commit introduces a caching bug that causes undesired collisions.

Fixes #150163 

MLIR bytecode does not preserve alias definitions, so each attribute
encountered during deserialization is treated as a new one. This can
generate duplicate `DISubprogram` nodes during deserialization.

The patch adds a `StringMap` cache that records attributes and fetches
them when encountered again.

- try_emplace(Key) is shorter than insert({Key, nullptr}).
- try_emplace performs value initialization without value parameters.
- We overwrite values on successful insertion anyway.

We already have hasOneUse. Like llvm::Value we provide helper methods to
query the number of uses of a Value. Add unittests for Value, because
that was missing.

---------

Co-authored-by: Michael Maitland <michaelmaitland@meta.com>

I observed that we have the boundary comments in the codebase like:

```
//===----------------------------------------------------------------------===//
// ...
//===----------------------------------------------------------------------===//
```

I also observed that there are incomplete boundary comments. The
revision is generated by a script that completes the boundary comments.

```
//===----------------------------------------------------------------------===//
// ...

...
```

Signed-off-by: hanhanW <hanhan0912@gmail.com>