Allow to use a sampling period of 1ms for the Polyglot Sampler

[eregon]

Currently, it seems that VisualVM enforces a period of 20ms when using the Polyglot Sampler.
This is quite imprecise, and often makes the profile less useful, especially if profiling for a short time or profiling a short script like bundle install on TruffleRuby for instance with a Gemfile like this:

source 'https://rubygems.org'
gem "path"

Could we make the period configurable, so it can be set to any value, down to 1ms?

BTW, --cpusampler defaults to a 1ms sample period, so this is well supported by CPUSampler:
https://github.com/oracle/graal/blob/9d21964f7afa35d4d4f3bece233a293b2682637e/tools/src/com.oracle.truffle.tools.profiler/src/com/oracle/truffle/tools/profiler/impl/CPUSamplerCLI.java#L94-L95

cc @norswap @chrisseaton

[jisedlac]

Implemented in master.

[eregon]

Thanks!