[WIP] recover fragment expression as assignment without rhs

When there is this source in a method:

```java
{
    ...
    "String".var
    ...
...
}
```

jdt.ui expects it to be recovered like this:

```java
{
    ...
    "String".var = $missing$;
    ...
```

Where `$missing$` is a fake, empty identifier.

Currently, in some cases, the `"String".var` is being completely
discarded, and this should improve that.

Signed-off-by: David Thompson <[email protected]>

Author: datho7561

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/parser/Parser.java

@@ -1138,6 +1138,13 @@ public RecoveredElement buildInitialRecoveryState(){
 	}
 
 	if (this.statementRecoveryActivated) {
+		if (this.expressionPtr >= 0 && this.expressionStack[0] instanceof FieldReference fr) {
+			var snr = new SingleNameReference(new char[0], fr.sourceEnd);
+			snr.sourceStart = fr.sourceEnd;
+			var assignment = new Assignment(fr, snr, fr.sourceEnd);
+			assignment.statementEnd = assignment.sourceEnd;
+			element = element.add(assignment, 0);
+		}
 		if (this.pendingRecoveredType != null &&
 				this.scanner.startPosition - 1 <= this.pendingRecoveredType.declarationSourceEnd) {
 			// Add the pending type to the AST if this type isn't already added in the AST.