[Java][MSF4J] Fix parameter names with {{baseName}}

[ePaul]

PR checklist

• Read the contribution guildelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change.
  → bin/java-msf4j-petstore-server.sh (once before the change (Update samples for MSF4J after 2.2.2. #4915) and once again after the change (with no effect)).
• Filed the PR against the correct branch: master for non-breaking changes.

Description of the PR

(This includes the changes from #4915. Should look better after merging this, or look at just the last commit. I'm already opening the PR so CI can look at it.) → now rebased.

This is a part of the fixes for meta issue #4898.

This fixes a wrong parameter mapping for file upload form parameters, as well as non-file-upload form parameters with the x-multipart vendor extension, when the parameter names in the OpenAPI definition get transformed to different names (e.g. to confirm to camelCase, or to avoid reserved words).

I didn't succeed to actually test this, not having a MSF4J project here.
The petstore example has no file upload form parameter where this would make a difference.

Needs review from Java/MSF4J experts. /cc @cbornet @xhh @kolyjjj

[ePaul]

Hmm, Travis seems to have problems with a network connection when installing NPM. :-/

[wing328]

@ePaul thanks for the fix.

@sanjeewa-malalgoda (creator of MSF4J generator), would you please take a look when you've time?

[ePaul]

(Rebased onto master to get rid of the commit from #4919.)