Add support for pedantic property access

[Kingwl]

Fixes #40170

[sandersn]

Some suggestions for the wording of messages.

[sandersn]

Also, at the Friday (Sep 4) design meeting, we decided not to create a single naming scheme for pedantic options, but (1) to name them for what they do (2) use the "no-" prefix only if it makes sense, since we already have some pedantic options named that, like noUnusedLocals, noFallthroughCasesInSwitch, etc.

I would suggest noPropertyAccessFromIndexSignature.

[andrewbranch]

Implementation looks good, @sandersn’s messaging suggestions look good

[ssledorze]

Really useful and awaited! :)
Looking forward to that PR being merged..
Is there some information on the expected release it would be part of?

[Kingwl]

@ssledorze After 4.1 release, I guess.

[sandersn]

I'll merge this after 4.1 RC.

[ssledorze]

I'll merge this after 4.1 RC.

should I understand it will be in the 4.1 release @sandersn ?

[sandersn]

No, we're finishing up 4.1 RC right now, then 4.1 will get its own branch. After that, commits to master will go into 4.2. So this will be in 4.2.

[Kingwl]

@typescript-bot pack this.

[typescript-bot]

Heya @Kingwl, I've started to run the tarball bundle task on this PR at 9fad505. You can monitor the build here.

[typescript-bot]

Hey @Kingwl, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/88073/artifacts?artifactName=tgz&fileId=1062C274A86E3AACC8BC8EC93C079C87B60E684E9F8015BD9366FD3BC705D07F02&fileName=/typescript-4.1.0-insiders.20201029.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build.

[typescript-bot]

The TypeScript team hasn't accepted the linked issue #40170. This makes it less likely that we'll review or accept this PR. Try to get the originating issue accepted.