Add 'exact' flag to arith.shrui/shrsi/divsi/divui operations (#165923)

This MR adds support for the `exact` flag to the
`arith.shrui/shrsi/divsi/divui` operations. The semantics are identical
to those of the LLVM dialect and the LLVM language reference.

This MR also modifies the mechanism for converting `arith` dialect
**attributes** to corresponding **properties** in the `LLVM` dialect.
(As a specific example, the integer overflow flags `nsw/nuw` are
**properties** in the `LLVM` dialect, as opposed to attributes.)

Previously, attribute converter classes were required to have a specific
method to support integer overflow flags:
```C++
template <typename SourceOp, typename TargetOp>
class AttrConvertPassThrough {
public:
  ...
  LLVM::IntegerOverflowFlags getOverflowFlags() const {
    return LLVM::IntegerOverflowFlags::none;
  }
};
```
This method was required, even for `arith` source operations that did
not use integer overflow flags (e.g. `AttrConvertFastMathToLLVM`).

This MR modifies the interface required by `arith` dialect attribute
converters to instead provide a (possibly NULL) properties attribute:
```C++
template <typename SourceOp, typename TargetOp>
class AttrConvertPassThrough {
public:
  ...
  Attribute getPropAttr() const { return {}; }
};
```
For `arith` operations with attributes that map to `LLVM` dialect
**properties**, the attribute converter can create a `DictionaryAttr`
containing target properties and return that attribute from the
attribute converter's `getPropAttr()` method. The `arith` attribute
conversion framework will set the `propertiesAttr` of an
`OperationState`, and the target operation's `setPropertiesFromAttr()`
method will be invoked to set the properties when the target operation
is created. The `AttrConvertOverflowToLLVM` class in this MR uses the
new approach.

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