refactor(yaml): rename util functions

[timreichen]

• renames _class() to getObjectTypeString()
• renames encodeHex() to charCodeToHexString()
• renames fromDecimalCode() to decimalCharCodeToNumber()
• renames fromHexCode() to hexCharCodeToNumber()

~All these functions are moved into _util.ts to clean up _loader.ts and _dumper.ts~

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.34146% with 3 lines in your changes missing coverage. Please review.

Project coverage is 95.81%. Comparing base (a92e1b6) to head (d809476).

Files	Patch %	Lines
yaml/_dumper.ts	80.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5310 +/- ## ======================================= Coverage 95.81% 95.81% ======================================= Files 458 458 Lines 37870 37877 +7 Branches 5566 5563 -3 ======================================= + Hits 36285 36292 +7 Misses 1545 1545 Partials 40 40 ```

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