buffer: DataView internals; BigInt read/write functions
new buffer functions: buf.{read|write}Big{U|UI}nt{64|128}[BL]E().
Also make new validator functions dealing with BigInt values for future use.
Checklist
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make -j4 test
(UNIX) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines