Typescript Fetch - Add support for file response type

[GabJac]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10)

Description of the PR

Changed the return type to a blob instead of json when the response type is a file.

[macjohnny]

@GabJac did you generate the samples and commit them?
Moreover, I believe it has already been resolved with #569 by @Place1
However, this PR is still useful, as it adds file support in the 3.x version.

[GabJac]

@macjohnny i did generate the samples but there was no change in them since there is no response of type file.

[macjohnny]

@GabJac thanks for checking. If nothing has changed, then it is fine.
I found a similar PR #1367. The main difference that I found is that it also reads the file name and modification date from the header and returns a File instance instead of a blob, am I right @spallister?
Maybe @TiFu @Place1 can give their opinion which of the two to use for 3.x.x?

[spallister]

Hey @macjohnny - Right you are.

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account