`built-ins/RegExp/property-escapes/non-existent-property-value-*` tests use invalid quantifiers, not non-existent property values

[auvred]

test262/test/built-ins/RegExp/property-escapes/non-existent-property-value-Script_Extensions.js

Line 18 in 7a2273a

/\\p{Script_Extensions=H_e_h}/u;

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Should be written as /\p{Script_Extensions=H_e_h}/u (with single /). Because /\\p{Script_Extensions=H_e_h}/ is interpreted as backslash \\ followed by p, repeated Script_Extensions=H_e_h times. Therefore, these tests are failing due to an invalid quantifier, not because of a non-existent property value.

It looks like this was missed in mathiasbynens/unicode-property-escapes-tests#9. Before this PR, there were calls like this:

assert.throws.early(SyntaxError, "/\\p{Script_Extensions=H_e_h}/u");

So, my assumption is that these tests were simply converted incorrectly to the new style.