omit_local_variable_types reports a false positive for a coerced integer literal

[eernstg]

Consider the following program:

void main() {
  double d = 1;
}

When omit_local_variable_types is enabled it reports that the type annotation double is unnecessary.

This is wrong because the value of the integer literal at run time is actually an instance of double, and if we change the context type to _ by removing the type annotation (and adding var or final) then its value will be an int, which may cause type errors below the declaration, and which is moreover an observable difference on some platforms at run time.

[eernstg]

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