fix(compiler-cli): suppress unnecessary optional chain for indexed accesses

[JoostK]

TypeScript's type system does not include undefined in the type of an indexed
access, whereas array index accesses may be expected to be out-of-bounds.
This commit updates the extended diagnostic for unnecessary optional chains to
ignore indexed accesses.

Closes #46918

[jelbourn]

Copying discussion we had on Slack:
My thinking was that for arrays, you should only get undefined out of an array in two conditions:

• a sparse array
• array index out of bounds

For sparse arrays, you should manually type your array to include | undefined.

For array index out of bounds, you want to throw a real error and not let the program silently propagate undefined.

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