This changes the function `resetToken` to not update `lastToken`.
The member `lastToken` is the last token that was consumed by the
parser.
Resetting the lexer position to a different position does not cause any
token to be consumed, so `lastToken` should not be updated.
Setting it to `curToken` can cause the scopeLoc.end location of
`OperationDefinition `to be off-by-one, pointing to the
first token after the operation.
An example for an operation for which the scopeLoc.end location was
wrong before is:
```
%0 = torch.vtensor.literal(dense_resource<__elided__> : tensor<768xbf16>) : !torch.vtensor<[768],bf16>
```
Here the scope end loc always pointed to the next token
This also adds a test for the Locations of `OperationDefinitions`.
Without the change to `resetToken` the test failes, with the scope end
location for `llvm.mlir.undef` pointing to the `func.return` in the next
line
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