blob: Add Upload and Download methods that may be more efficient for some drivers

[vangent]

Fixes #3245
Fixes #2807

[codecov]

Codecov Report

Merging #3248 (7234410) into master (0cc16c8) will decrease coverage by 0.03%.
The diff coverage is 72.30%.

@@            Coverage Diff             @@
##           master    #3248      +/-   ##
==========================================
- Coverage   77.37%   77.34%   -0.03%     
==========================================
  Files         103      103              
  Lines       13550    13599      +49     
==========================================
+ Hits        10484    10518      +34     
- Misses       2337     2346       +9     
- Partials      729      735       +6     

Impacted Files	Coverage Δ
blob/driver/driver.go	66.66% <ø> (ø)
blob/memblob/memblob.go	93.29% <ø> (+0.23%)	⬆️
blob/s3blob/s3blob.go	90.00% <ø> (+0.25%)	⬆️
blob/blob.go	87.10% <60.00%> (-2.04%)	⬇️
blob/azureblob/azureblob.go	87.28% <90.90%> (+0.45%)	⬆️
blob/fileblob/fileblob.go	82.09% <100.00%> (+0.11%)	⬆️

... and 2 files with indirect coverage changes