Adds a error diagnostic with newlines if either source or target are longer than 30 characters on type is not assignable to type

[orta]

Fixes #45896 - this keeps the formatting I recommended in that issue, but that doesn't have to be the answer:

// a is 31 chars long
let a = { b: { c: { e: { f: 123 } } } };
let b = "hello"

b=a

Gives:

Type:
{ b: { c: { e: { f: number; }; }; }; }

is not assignable to type:
string

Which is the simplest version of this PR via diagnostics, there's space here for a few answers which I can look at (having 3 diags, 1 with newlines for source, 1 with newlines for target, 1 with newlines for both)

[orta]

I'm not too convinced on indenting unless there is more whitespace:

Type:
  { b: { c: { e: { f: number; }; }; }; }

is not assignable to type:
  string

feels tight to me?

Yet:

Type:

  { b: { c: { e: { f: number; }; }; }; }

is not assignable to type:

  string

Feels a bit too whitespacey though? But open to ideas

[fbartho]

I like the indenting personally, not the extra newlines.

eg. (I prefer this:)

Type:
  { b: { c: { e: { f: number; }; }; }; }

is not assignable to type:
  string

[Assuming you wanted bike shedding opinions 😉]

[vdawg-git]

This looks great! The indents are nice, but extra lines do indeed add too much whitespace.

[sandersn]

I like this but @DanielRosenwasser should also sign off.

[sandersn]

I'm going to close this PR for two reasons:

• We don't have time to add/review new features until we switch to Corsa, at which point this will have to be rewritten in Go.
• The PR is extremely out of date now.

We should revisit this after Corsa is ready.