Tuple should be readonly by default

Any tuples can mutate, this entails incorrect typing

TypeScript Version: 4.1.0-dev.20200828

Search Terms:
"readonly tuple"
"immutable tuple"

Code

const exampleSort: [number, string] = [2, '1'];

exampleSort.sort();

exampleSort // Type: [number, string], RealType: [string, number]

const exampleSplice: [number, string] = [2, '1'];

exampleSplice.splice(0, 1);

exampleSplice // Type: [number, string], RealType: [string]

Expected behavior:

const exampleSort: [number, string] = [2, '1'];

// Property 'sort' does not exist on type '[number, string]'.(2339)
exampleSort.sort();

const exampleSplice: [number, string] = [2, '1'];

// Property 'splice' does not exist on type '[number, string]'.(2339)
exampleSplice.splice(0, 1);

Actual behavior:

const exampleSort: [number, string] = [2, '1'];

exampleSort.sort();

const exampleSplice: [number, string] = [2, '1'];

exampleSplice.splice(0, 1);

Playground Link: https://www.typescriptlang.org/play?ts=4.1.0-dev.20200828#code/MYewdgzgLgBApgDwIYFsAOAbOBlEAnKALhgG0wBXFAIzjwBoZo8BLMAcwF0YBeUgJgYByAIyCOAbgBQkxKkw58UAHQRFACgCUUmcnRZcBGAHojMACoBPNHGJlKNeoygt2HBgCU4SDJeu2mrGwMFNS0HNKgkLCyejiYzMA2pCEODAGuPPxCohLSMfLY8YkqRXBqAAwMwlp5ugWlxqa+SXahjumcHl4+Vi0d4dKSQA

Related Issues:

Start by reproducing the tuple examples in the linked TypeScript Playground and compare the reported types with the runtime mutations from sort and splice. Trace the compiler's tuple and array mutability handling; done means the expected diagnostics appear for these operations without breaking valid tuple usage.