Support ECMAScript private fields added from TS 3.8

[rhysd]

ECMAScript private fields spec was implemented in TypeScript and released at v3.8 beta.

microsoft/TypeScript#33925

class C {
    #foo = 10;
    bar = true;

    piyo() {
        return this.#foo;
    }
}

• Previously the private name field declaration #foo in #foo = 10 was not highlighted. This PR adds highlight to it
• Now '#' is part of identifiers in TypeScript. So this PR adds it to iskeyword option. Vim can recognize #foo as one identifier by it.

[HerringtonDarkholme]

Thanks!

[NullVoxPopuli]

are private methods a thing?

[rhysd]

I did not care methods.

[rhysd]

I checked TypeScript 3.8 RC, but it does not support private methods. It's private 'fields' so it does not include methods.

I tried:

class Foo {
    #foo() {
        console.log('hi');
    }
    show() {
        this.#foo();
    }
}

and I got:

foo.ts:2:5 - error TS18022: A method cannot be named with a private identifier.

2     #foo() {
      ~~~~


Found 1 error.

[HerringtonDarkholme]

Hi @NullVoxPopuli, it won't be hard to add private method support once it is available in TypeScript.
Let's wait for its adoption.