Introduce Word128 integer type

[darkdrag00nv2]

Work towards #2389
Work towards onflow/developer-grants#179

Description

This PR introduces the type Word128 to Cadence.

---

• 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 #2497 (d3de346) into master (ed98581) will decrease coverage by 0.11%.
The diff coverage is 62.88%.

@@            Coverage Diff             @@
##           master    #2497      +/-   ##
==========================================
- Coverage   78.55%   78.45%   -0.11%     
==========================================
  Files         336      336              
  Lines       76044    76561     +517     
==========================================
+ Hits        59739    60068     +329     
- Misses      14099    14262     +163     
- Partials     2206     2231      +25     

Flag	Coverage Δ
unittests	78.45% <62.88%> (-0.11%)	⬇️

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

Impacted Files	Coverage Δ
encoding/ccf/traverse_value.go	98.30% <ø> (ø)
runtime/interpreter/hashablevalue.go	100.00% <ø> (ø)
runtime/interpreter/primitivestatictype_string.go	100.00% <ø> (ø)
runtime/interpreter/visitor.go	8.51% <0.00%> (-0.19%)	⬇️
runtime/interpreter/value.go	69.08% <53.54%> (-0.46%)	⬇️
runtime/interpreter/encode.go	67.27% <66.66%> (-0.01%)	⬇️
types.go	85.66% <66.66%> (-0.13%)	⬇️
encoding/json/decode.go	88.33% <68.75%> (-0.32%)	⬇️
runtime/interpreter/decode.go	46.61% <70.58%> (+0.27%)	⬆️
values.go	76.08% <80.00%> (+0.10%)	⬆️
... and 13 more

[turbolent]

Nice!

[SupunS]

Nice work!

[darkdrag00nv2]

Had to force push after resolving merge conflicts.

[turbolent]

Nice!