Fix fontification TypeScript of import-statements (bug#61081)

Fix fontification TypeScript of import-statements (bug#61081)

Currently typescript-ts-mode and tsx-ts-mode handles imports with
aliases incorrectly.

Consider the following case:

import { someFunc as someAlias } from "module";

In this case the entire import ("someFunc as someAlias") will be
highlighted as a variable name. "as" is also highlighted as a
variable, rather than a reserved keyword.

To be consistent with how we otherwise do things, we should only
highlight the variable which is new and/or introduced, in this case
"someAlias".

Attached is a patch which fontifies import-declarations somewhat more
correctly.

The following cases have been tested and all fontify properly:

import gnu from "fsf";              // highlights gnu
import { gnu2 } from "fsf2";        // highlights gnu2
import { gnu as gnu3 } from "fsf3"; // highlights gnu3
import * as gnu4 from "fsf4";       // highlights gnu4

* lisp/progmodes/typescript-ts-mode.el
(typescript-ts-mode--font-lock-settings): Tweak import_clause rules to
adhere to the comment above.