This patch is part of a project to move the Presburger library into
LLVM.

This commit enables the expression of negated native constraints in PDLL:

If a constraint is prefixed with "not" it is parsed as a negated constraint and hence the attribute `isNegated` of the emitted `pdl.apply_native_constraint` operation is set to `true`.
In first instance this is only supported for the calling of external native C++ constraints and generation of PDL patterns.

Previously, negating a native constraint would have  been handled by creating an additional native call, e.g.
```PDLL
Constraint checkA(input: Attr);
Constarint checkNotA(input: Attr);
```
or by including an explicit additional operand for negation, e.g.
`Constraint checkA(input: Attr, negated: Attr);`

With this a constraint can simply be negated by prefixing it with `not`. e.g.
```PDLL
Constraint simpleConstraint(op: Op);

Pattern example {
    let inputOp = op<test.bar>() ->(type: Type);
    let root = op<test.foo>(inputOp.0) -> ();
    not simpleConstraint(inputOp);
    simpleConstraint(root);
    erase root;
}
```

Depends on [[ https://reviews.llvm.org/D153871 | D153871 ]]

Reviewed By: Mogball

Differential Revision: https://reviews.llvm.org/D153959

We currently aren't handling this properly, and in the case
of a string block just crash. This commit adds proper error handling
and detection for eof.

Differential Revision: https://reviews.llvm.org/D124585

This allows for providing completion results for include directive
file paths by searching the set of include directories for the current
file.

Differential Revision: https://reviews.llvm.org/D124112

This allows for navigating to included files on click, and also provides hover
information about the include file (similarly to clangd).

Differential Revision: https://reviews.llvm.org/D124077

This commit adds code completion support to the language server,
and initially supports providing completions for: Member access,
attributes/constraint/dialect/operation names, and pattern metadata.

Differential Revision: https://reviews.llvm.org/D121544

These functions allow for defining pattern fragments usable within the `match` and `rewrite` sections of a pattern. The main structure of Constraints and Rewrites functions are the same, and are similar to functions in other languages; they contain a signature (i.e. name, argument list, result list) and a body:

```pdll
// Constraint that takes a value as an input, and produces a value:
Constraint Cst(arg: Value) -> Value { ... }

// Constraint that returns multiple values:
Constraint Cst() -> (result1: Value, result2: ValueRange);
```

When returning multiple results, each result can be optionally be named (the result of a Constraint/Rewrite in the case of multiple results is a tuple).

These body of a Constraint/Rewrite functions can be specified in several ways:

* Externally
In this case we are importing an external function (registered by the user outside of PDLL):

```pdll
Constraint Foo(op: Op);
Rewrite Bar();
```

* In PDLL (using PDLL constructs)
In this case, the body is defined using PDLL constructs:

```pdll
Rewrite BuildFooOp() {
  // The result type of the Rewrite is inferred from the return.
  return op<my_dialect.foo>;
}
// Constraints/Rewrites can also implement a lambda/expression
// body for simple one line bodies.
Rewrite BuildFooOp() => op<my_dialect.foo>;
```

* In PDLL (using a native/C++ code block)
In this case the body is specified using a C++(or potentially other language at some point) code block. When building PDLL in AOT mode this will generate a native constraint/rewrite and register it with the PDL bytecode.

```pdll
Rewrite BuildFooOp() -> Op<my_dialect.foo> [{
  return rewriter.create<my_dialect::FooOp>(...);
}];
```

Differential Revision: https://reviews.llvm.org/D115836

These are used pervasively during parsing.

Differential Revision: https://reviews.llvm.org/D118291