sanitize id paths via base64 encoding

[arifogel]

• supports relaxed restrictions on entity names
• prevents malicious path injection

[batfish-bot]

This change is 

[codecov]

Codecov Report

Merging #5740 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #5740      +/-   ##
============================================
- Coverage     71.40%   71.40%   -0.01%     
+ Complexity    33680    33671       -9     
============================================
  Files          2788     2788              
  Lines        139584   139590       +6     
  Branches      16790    16790              
============================================
- Hits          99673    99670       -3     
- Misses        32046    32052       +6     
- Partials       7865     7868       +3     

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/org/batfish/storage/FileBasedStorage.java	82.53% <ø> (ø)	145.00 <0.00> (ø)
...a/org/batfish/identifiers/FileBasedIdResolver.java	86.45% <100.00%> (+0.90%)	44.00 <4.00> (ø)
.../src/main/java/org/batfish/datamodel/flow/Hop.java	53.33% <0.00%> (-6.67%)	5.00% <0.00%> (-1.00%)
...c/main/java/org/batfish/dataplane/rib/RibTree.java	89.58% <0.00%> (-4.17%)	27.00% <0.00%> (-1.00%)
...org/batfish/datamodel/flow/BidirectionalTrace.java	81.81% <0.00%> (-2.28%)	14.00% <0.00%> (-1.00%)
...src/main/java/org/batfish/coordinator/PoolMgr.java	64.04% <0.00%> (-1.13%)	15.00% <0.00%> (-1.00%)
...rg/batfish/dataplane/ibdp/EigrpRoutingProcess.java	92.72% <0.00%> (-0.39%)	68.00% <0.00%> (-1.00%)
...java/org/batfish/dataplane/ibdp/VirtualRouter.java	88.04% <0.00%> (-0.32%)	262.00% <0.00%> (-2.00%)

[dhalperi]

Reviewed 5 of 5 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved