Add an experimental tools-typescript package for better react-native builds with typescript

[JasonVMo]

Description

A package that helps with building typescript, particularly for react-native. It
leverages the @rnx-kit/typescript-service package to build using the language
service rather than using the compiler directly. This allows for custom
resolution strategies (among other things). The compilation and type-checking
are still done by typescript but this drives some convenient custom
configurations.

In particular the buildTypescript command can do things like:

• multiplex a build in a directory, to build for multiple react-native platforms
  at the same time. The files will be split such that the minimal build can be
  performed.
• detect which react-native platforms should be built based on rnx-kit bundle
  configs or react-native.config.js settings.
• successfully build with the module suffixes without throwing up a ton of bogus
  unresolved reference errors.
• share caches where possible to speed up compilations within the same node
  process.

Motivation

The current story for building typescript for react-native is sub-par, and
typescript itself is particularly restrictive with module resolution. This
addresses the ability to build react-native better right now, but also creates a
framework for experimenting with different resolvers.

Test plan

• There are some unit tests already but more will be added in the future.
• Tested via repo linking in the FURN repo since it has complex build needs
• Planning to add a test repo for another change and will run builds in there and compare results with tsc as part of validation.

[tido64]

Sorry, didn't mean to approve this already.

[JasonVMo]

Sorry, didn't mean to approve this already.

No worries, wouldn't submit without hearing back anyways. I just submitted changes in response to your comments. Two still warrant a bit of discussion.