Prevent ABI objects from being mutated

[haltman-at]

Description

Fixes #3748. Prevents ABI parameter objects from being changed when used as inputs to encoding/decoding functions. Does this by replacing t.type = "bytes24" with t = Object.assign({}, t, { type: "bytes24" }).

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build and tested dist/web3.min.js in a browser.
• I have tested my code on the live network.
• I have checked the Deploy Preview and it looks correct.
• I have updated the CHANGELOG.md file in the root folder.

[haltman-at]

I had trouble completing some of the checklist on my machine (and am still running some of it which I'll check off later), but since this is so simple I hope that's OK.

[haltman-at]

Btw tagging @cgewecke and @GregTheGreek to make sure you two see this. :)

[coveralls]

Coverage decreased (-2.4%) to 78.034% when pulling fd717ba on haltman-at:no-mutate into 4469516 on ethereum:1.x.

[GregTheGreek]

@spacesailor24 cant seem to assign you...