Fix and enhance mulitple quoted string issues

[msftrncs]

• Fixes Double doublequotes in here-string scopes as a character.escape #143, moving the double double-quote escape ("") in to doubleQuotedString from doubleQuotedStringEscapes, and removing the double single-quote escape ('') from the pattern for single quoted here-strings.

• Fixes Quoted strings/here-strings issues #167 (entirely), permitting white space to follow the opening token for here-strings, adding punctuation scopes to the start and end tokens (punctuation.definition.string…), and preparing some of the string regex's for the following change.

• Closes Account for curly quotes in syntax definition. #141, applying the PowerShell supported curly quotes \x{2018}-\x{201B} (single quotes) and \x{201C}-\x{201E} (double quotes), everywhere except for an occurrence in hashtable:

  EditorSyntax/PowerShellSyntax.tmLanguage

  Lines 1501 to 1504 in 44eac87

  	<key>match</key>
  	<string>\b((?:\'|\")?)(\w+)((?:\'|\")?)(?:\s+)?(=)(?:\s+)?</string>
  	<key>name</key>
  	<string>meta.hashtable.assignment.powershell</string>

  There are issues in this area, that nearly make the quotes in this section unusable.

• Tests added for single quoted here-string, and the escaping issue of Double doublequotes in here-string scopes as a character.escape #143. There are currently no tests I found for punctuation.definition.string… for any kind of strings.