Use StandardCharsets instead of charset names

[bencomp]

What this PR does / why we need it: This fixes a (potential) resource leak as described in #10053 and it replaces all uses of "utf-8", "us-ascii" and "iso-8859-1" (mostly in upper case though) to get a charset with StandardCharsets.X. The constants in StandardCharsets are supported on all Java implementations (since its introduction), so using them in String.getBytes(..) will not throw an UnsupportedEncodingException. This may simplify the code.

Which issue(s) this PR closes:

Closes #10076 Closes #10053

Special notes for your reviewer: Apologies for mixing these two issues in one PR.

Suggestions on how to test this: See that the test suites pass.

Does this PR introduce a user interface change? If mockups are available, please link/include them here: No

Is there a release notes update needed for this change?: No

Additional documentation: Also linked from #10076, Sonarcloud's explanation for using StandardCharsets may be helpful.