Add synchronization around SDLResponseDispatcher

[joeljfischer]

Fixes #1515

This PR is ready for review.

Risk

This PR makes no API changes.

Testing Plan

• I have verified that I have not introduced new warnings in this PR (or explain why below)
• I have run the unit tests with this PR
• I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).

Unit Tests

No unit tests were added, they were run and pass.

Core Tests

• Tested example app with numerous menu cells, submenu cells, soft buttons, etc. to stress test RPCs waiting for synchronization.

Core version / branch / commit hash / module tested against: Sync 3.0 (19205_DEVTEST), Manticore v2.4.2 (SDL Core v6.0.1)
HMI name / version / branch / commit hash / module tested against: Sync 3.0 (19205_DEVTEST), Manticore v2.4.2 (Generic HMI v0.7.2.)

Summary

• Methods that alter the internal dictionaries and map tables of the SDLResponseDispatcher are now synchronized.

Changelog

Bug Fixes

• Fix concurrent setting to dictionaries and map tables causing crashes by synchronizing setter access.

CLA

• I have signed the CLA

[NicoleYarroch]

Left some comments

[NicoleYarroch]

I am getting anything random failing test cases (between 3 and 8 total) in SDLResponseDispatcherSpec.

[NicoleYarroch]

Left a comment about failing test cases

[joeljfischer]

There were issues due to directly accessing properties for a value that was stored in storeRequest: which stores it asynchronously. I re-did the tests to be "eventually" instead.