Lint against re-declaring parameters

[nicolo-ribaudo]

Linting for tc39/ecma262#3768. This is probably not going to catch every single case, but it should catch the majority.

With this change we get a false positive in ValidateAndApplyPropertyDescriptor step 6.c.i:

1. For each field of _Desc_, set the corresponding attribute of the property named _P_ of object _O_ to the value of the field.

because Desc is the first variable defined after for each, so ecmarkup thinks that we are re-declaring it. It would report the same error for this algorithm, even if Desc was not a parameter:

1. Let _Desc_ be SomehowGetDesc()
1. For each field of _Desc_, set the corresponding attribute of the property named _P_ of object _O_ to the value of the field.

If we want to lint for re-declared parameters, we can update that loop to instead do something like

1. For each field name _F_ of _Desc_, set the attribute _F_ of the property named _P_ of object _O_ to the value of the field.

so that ecmarkup doesn't think that that step is declaring Desc.

[bakkot]

The change to ValidateAndApplyPropertyDescriptor SGTM. Want to open and land that change first, then we can land this?