feat!: add encode/decodeValueType as public callable methods

[CJ42]

What kind of change does this PR introduce (bug fix, feature, docs update, ...)?

Feature

What is the current behaviour (you can also link to an open issue here)?

The methods encodeValueType and decodeValueType are currently not available as public method part of the ERC725 class.

These methods can be useful to encode certain LSP2 value type raw. For example, a uin128 (For LSP2 Array length) to obtain an exactly 16 bytes long value.

What is the new behaviour (if this is a feature change)?

Make this method part of the class, so that they can be called and used.

Other information:

[frozeman]

we need to update the docs as well, when we do this change

[Hugoo]

Ready to merge - just waiting for conflict fix and docs update: https://github.com/ERC725Alliance/erc725.js/blob/develop/docs/classes/ERC725.md

[codecov-commenter]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (9640d9f) 83.71% compared to head (1c6925a) 83.50%.
Report is 19 commits behind head on develop.

Files	Patch %	Lines
src/lib/encoder.ts	73.68%	0 Missing and 5 partials ⚠️
src/index.ts	63.63%	4 Missing ⚠️
src/lib/getDataFromExternalSources.ts	33.33%	0 Missing and 2 partials ⚠️
src/lib/utils.ts	81.81%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #325      +/-   ##
===========================================
- Coverage    83.71%   83.50%   -0.21%     
===========================================
  Files           18       17       -1     
  Lines         1130     1134       +4     
  Branches       255      258       +3     
===========================================
+ Hits           946      947       +1     
+ Misses          98       97       -1     
- Partials        86       90       +4     

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[CJ42]

@Hugoo this has not been deleted, just move at the top to sort function names correctly by alphabetical order.