doc: clarify FileHandle error handling

[bobu-putheeckal]

Fixes: #51135

This clarifies that filehandle.close() and filehandle.stat() promises may reject when the underlying file system operation fails, and points readers to Common System Errors for code values.

Evidence checked:

• FileHandle.prototype.stat() calls fsCall(fstat, this, options) in lib/internal/fs/promises.js.
• fstat() uses binding.fstat(..., kUsePromises) and routes binding failures through handleErrorFromBinding.
• FileHandle::ClosePromise() in src/node_file.cc documents that the close promise rejects with a UVException if closing the fd fails.
• The linked issue includes a maintainer example showing filehandle.stat() rejecting with EBADF after the handle is closed.

Validation:

• git diff --check
• node tools/lint-md/lint-md.mjs doc/api/fs.md
• npx -q core-validate-commit --no-validate-metadata --tap HEAD

[trivikr]

The linked section is explicitly non-exhaustive and does not include EBADF, which is one failure filehandle.stat() can return. We should avoid promising that every code appears there.

Suggested change

	The promise is rejected if closing the file handle fails. In case of an error,
	the error's `code` will be one of [Common System Errors][].
	The promise is rejected if closing the file handle fails. The error's `code`
	identifies the platform-dependent system error; see [Common System Errors][]
	for examples.

Please make the equivalent change in the filehandle.stat() occurrence below as well.