feat(ts-estree): add preserveNodeMaps option

[JamesHenry]

I have been working on converting some user-land custom TSLint rules to ESLint and this feature has come from that work.

• In many cases, I am discovering migrating custom TSLint rules to ESLint is far easier if you first migrate the "infrastructure" over (all the rule and RuleTester config), but keep the rule logic largely the same. (With the idea that you can truly migrate the implementation at some point later).

• Naturally, this is only possible if you have access to the two-way AST node maps that may be preserved during conversion.

• Preserving the AST node maps is currently only possible if using the project option. This is a good start, but as we know the project feature is expensive because of its requirement to create full TypeScript Programs.

• If a custom TSLint rule only requires syntactic information, it is completely unnecessary to create a full Program.

This PR introduces a new option for typescript-estree which allows for the user to explicitly control whether or not AST node maps are preserved during conversion.

There will be follow up PRs where I add utilities I have created for ESLint rules which meet the above criteria (e.g.getNodeMaps()), but I wanted to add the flag itself in a dedicated PR.

(NOTE: for backwards compatibility the existing behaviour around project causing node maps to be preserved has been maintained here)

[codecov]

Codecov Report

Merging #494 into master will increase coverage by 0.06%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #494      +/-   ##
==========================================
+ Coverage   95.75%   95.81%   +0.06%     
==========================================
  Files          77       77              
  Lines        3484     3489       +5     
  Branches      960      963       +3     
==========================================
+ Hits         3336     3343       +7     
  Misses         51       51              
+ Partials       97       95       -2

Impacted Files	Coverage Δ
packages/typescript-estree/src/ast-converter.ts	100% <100%> (ø)	⬆️
packages/typescript-estree/src/convert.ts	98.96% <100%> (ø)	⬆️
packages/typescript-estree/src/parser.ts	95% <88.88%> (+2.01%)	⬆️

[JamesHenry]

@j-f1 Taking your thumbs up emojis on here and slack as an approval review 😛