Add a new set of APIs for JIT configuration.

Add a new set of APIs for JIT configuration.

These APIs accommodate the retrieval of config values using the JIT
interface rather than the utilcode library. All configuration options
are now initialized upon the first call to compileMethod. The values
of configuration options are available off of an ambient JitConfig
object.

This also changed `JitHost::get*ConfigValue` to use the
`EEConfig_default` policy instead of `REGUTIL_default` in order to
avoid breaking a small set of JIT config options available in release
builds that were using the former. This change is exceedingly
unlikely to adversely affect the behavior of other JIT config options
that were originally fetched using `REGUTIL_default`, since values
for these options should not be present any locations searched
by `EEConfig_default` that are not searched by
`REGUTIL_default` (namely config files).

[tfs-changeset: 1578859]

Commit migrated from https://github.com/dotnet/coreclr/commit/d2b9a6e8bae487ae092fca2d3bccd109c7ef85f9