Remove support for importing/exporting and JSON encoding/decoding path links and cadence type

[turbolent]

Closes #2208
Closes #2167

Description

#260 has added support for importing/exporting path link values into/from the interpreter, as well as encoding to/decoding from JSON.

This was likely only done because the Playground rendered storage contents in its UI by exporting stored values. Since then, storage inspection has changed and does not rely on this feature anymore.

Path links are only stored in storage, but are not first-class values.
Remove

• cadence type definition
• Interpreter import/export
• JSON encoding/decoding

---

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov]

Codecov Report

Merging #2248 (c94c080) into master (4be8295) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2248      +/-   ##
==========================================
- Coverage   77.70%   77.69%   -0.02%     
==========================================
  Files         309      309              
  Lines       65815    65793      -22     
==========================================
- Hits        51142    51116      -26     
- Misses      12895    12898       +3     
- Partials     1778     1779       +1     

Flag	Coverage Δ
unittests	77.69% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
encoding/json/decode.go	88.12% <ø> (-0.06%)	⬇️
encoding/json/encode.go	94.42% <ø> (-0.11%)	⬇️
runtime/convertValues.go	82.88% <ø> (-0.13%)	⬇️
values.go	66.59% <ø> (-0.04%)	⬇️
runtime/environment.go	90.73% <0.00%> (-1.47%)	⬇️

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[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit 2ed0f28
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -benchmem -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Collapsed results for better readability