tslib should be put in dependencies

[zhaoyao91]

Current Behavior

Currently the tslib is put in devDependencies, but as importHelpers is true in tsconfig.json, the build result will only require tslib. In some build context, such as in electron, the tslib will not be packaged since it is not in dependencies.

Suggested solution(s)

Two options:

• importHelpers set to false
• or, add tslib as dependencies instead of dev dependencies

Your environment

Software	Version(s)
TSDX	0.12.0

[agilgur5]

This was a regression caused by #130 and fixed in #415, related to #413

TSDX transpiles TS -> ESNext, then ESNext -> preset-env, so Babel's helper functions get generated instead of TS ones.

There's still some debate about whether those should import from @babel/runtime (instead of being duplicated between libraries) by default or not, but currently they don't.