Optimize JPG.js receiveAndExtend for 1 bit case.

Profiling showed that receiveAndExtend is frequently called with the length of
one bit. This happens for example in decodeBaseline.
For a single bit, the loop and shift in receive, as well as the shifts in
receiveAndExtend are overhead.
This shortcut manually calculates the shifts by either returning 1 or -1 from
receiveAndExtend by reading the bit and deciding on the return value.
While it comes with an overhead for each non-one length, the speedup is at about
10% in the hot parse/decode path.
Deleted unused variables in jpgjs buildComponentData.
Merge pull request #4894 from CodingFabian/optimize-jpgjs-receiveAndExtend

Optimize JPG.js receiveAndExtend for 1 bit case.
Merge pull request #4896 from CodingFabian/cleanup-jpgjs-buildComponentData

Deleted unused variables in jpgjs buildComponentData.
Optimization for FlateStream_getCode, making more pdfs parsable.

This commit cleans up the FlateStream_getCode method, and removes a few error
conditions.
Previously it would fail if the codeSize is less than maxLen if end of stream
is reached. However in the document linked below there is a sub-stream
(the one starting at pos 337) which has maxLen set to 11, but actually
contains only 10. After breaking the sanity check still applies, and in this
case passes validating codeSize(10)==codeLen(10).

 http://www.cafeculture.com/wp-content/uploads/2014/03/V-CM-BR-086-04002-1346-0258-GP-Brazil-Fazenda-Cafe-Cambara-Terra-Preta-Microlot-Sample-0460-13-Pulped-Natural-60Kg.pdf
Merge pull request #4897 from CodingFabian/optimize-stream-getCode

Optimization for FlateStream_getCode, making more pdfs parsable.
Optimized Lexer_getObj 2x faster
utils.js optimization of isFOO methods
evaluator.js minor optimizations
Optimized CanvasGraphics_executeOperatorList 66% faster
canvas.js minor optimizations
Optimized genericComposeSMask

Declaring the composition and backgdrop functions outside of genericComposeSMask
is more efficient.
Minor refactoring of EvaluatorPreprocessor_read