Bad prototypes for String, Number and Boolean

[tofpie]

Describe the bug
The prototypes for String, Number and Boolean should be respectively String(""), Number(0) and Boolean(false).

To Reproduce
This JavaScript code reproduces the issue:

>> String.prototype.toString()
Uncaught: "TypeError": "'this' is not a string"
>> Number.prototype.toString()
Uncaught: "TypeError": "'this' is not a number"
>> Boolean.prototype.toString()
Uncaught: "TypeError": "'this' is not a boolean"

Expected behavior

>> String.prototype.toString()
""
>> Number.prototype.toString()
"0"
>> Boolean.prototype.toString()
"false"

Build environment

• OS: Windows 10
• Version: 0.10
• Target triple: x86_64-pc-windows-msvc
• Rustc version: rustc 1.48.0 (7eac88abb 2020-11-16)

Additional context
String prototype specification
Number prototype specification
Boolean prototype specification