Make InterningBinaryReader pool buffers

[ladipro]

Fixes #3954

Context

The Buffer class is 100 kB (40 for characters and 60 for the byte array) and it is being allocated a lot, easily in the order of tens of thousands of instances per build. OOM crashes are often blamed on such allocations.

Changes Made

1. Made the byte array allocation lazy since in many scenarios it ends up not being used.
2. Implemented a trivial Buffer pooling which eliminates >97% of allocations.

Testing

• Existing unit tests.
• Experimental VS insertion.

Notes

Opted for a 1-element static cache to keep the last used Buffer around. This works very well given MSBuild's single-threadedness and keeps the code simple and policy-free.

[ladipro]

RPS is showing ~6% improvement in allocated devenv bytes during rebuild. Will address the failing unit test shortly.

[rokonec]

Please consider commenting static internal ITranslator GetReadTranslator(Stream stream, SharedReadBuffer buffer) and explain consequences and behavior of null buffer passing.
NIT: I would recommend introducing static internal ITranslator GetReadTranslatorUsingPooledBuffer(Stream stream)