Request member collision

[sbiscigl]

Description of changes:

Duplicate of a existing PR with a bug fix on top. Original PR

From the original PR

We do this beacuse the C++ SDK has a design flaw: Model fields and request fields are mixed
in a single object. Practically this means that if a request has a field called headers, the SDK will
generate a method called GetHeaders, which clashes with the GetHeaders method to get access to the
HTTP request headers.
This method will substitute headers for headerValues so we end up with a GetHeaderValues
method. This is still going to be confusing for the end user but it's the best I can think of right now.

From that PR we had a conversation and noticed serveral things. First we changed the PR to capture more member values that might collide on request objects, and realized that api gateway has a entire custom generator to get around what the issue was. So making a general case can remove this customization in the future and prevent further customizations.

This also revealed a current bug where location name was not getting set correctly for the renaming of shapes in json services, that revealed deserialization of GetGeneratedPolicyResult.cpp was actually broken because of the rename.

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• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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