Make interfaces Serializable

[danieldietrich]

Fixes #1810

[danieldietrich]

Matches before instanceOf(Traversable.class) is checked, so it is ok.

[danieldietrich]

In 3.0.0 Iterator will not implement Traversable any more (i.e. all internal ofAll(iterator) calls will be substituted with ofAll(() -> iterator)). So all Traversables will be Serializable.

[codecov-io]

Codecov Report

Merging #1892 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #1892      +/-   ##
============================================
+ Coverage     98.07%   98.09%   +0.01%     
- Complexity     5051     5052       +1     
============================================
  Files            88       88              
  Lines         11401    11401              
  Branches       1503     1503              
============================================
+ Hits          11182    11184       +2     
+ Misses          113      112       -1     
+ Partials        106      105       -1

Impacted Files	Coverage Δ	Complexity Δ
...aslang/src/main/java/javaslang/collection/Seq.java	95% <ø> (ø)	50 <0> (ø)	❌
...rc/main/java/javaslang/collection/Traversable.java	96.53% <ø> (ø)	103 <0> (ø)	❌
...aslang/src/main/java/javaslang/control/Option.java	100% <ø> (ø)	42 <0> (ø)	❌
...g/src/main/java/javaslang/collection/Multimap.java	96.61% <ø> (ø)	26 <0> (ø)	❌
...aslang/src/main/java/javaslang/collection/Map.java	97.91% <ø> (ø)	32 <0> (ø)	❌
...slang/src/main/java/javaslang/collection/Tree.java	97.78% <ø> (ø)	113 <0> (ø)	❌
...aslang/src/main/java/javaslang/control/Either.java	100% <ø> (ø)	38 <0> (ø)	❌
...aslang/src/main/java/javaslang/collection/Set.java	75% <ø> (ø)	3 <0> (ø)	❌
javaslang/src/main/java/javaslang/control/Try.java	94.14% <ø> (ø)	76 <0> (ø)	❌
...ng/src/main/java/javaslang/control/Validation.java	99.04% <100%> (ø)	54 <0> (ø)	❌
... and 1 more

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