Add missing UNDNAME_ flags

[DaZombieKiller]

This PR adds the following new constants to um/DbgHelp/Windows.Manual.cs:

• UNDNAME_RESERVED1 (0x0020)
• UNDNAME_RESERVED2 (0x0040)
• UNDNAME_TYPE_ONLY (0x2000)
• UNDNAME_HAVE_PARAMETERS (0x4000)
• UNDNAME_NO_ECSU (0x8000)
• UNDNAME_NO_IDENT_CHAR_CHECK (0x10000)
• UNDNAME_NO_PTR64 (0x20000)

As far as I am aware, these are not present in any public headers. However, they are documented in at least two places:

• IDiaSymbol::get_undecoratedNameEx's documentation page:

The flag names are not defined in the DIA SDK, so you need to either add the declarations to your code or use the raw values.

• The output of undname.exe -show_flags:

Microsoft (R) C++ Name Undecorator
Copyright (C) Microsoft Corporation. All rights reserved.

Usage: undname [flags] fname [fname...]
   or: undname [flags] file

where flags are the following OR'd together:

0x0001  Remove leading underscores from Microsoft extended keywords
0x0002  Disable expansion of Microsoft extended keywords
0x0004  Disable expansion of return type for primary declaration
0x0008  Disable expansion of the declaration model
0x0010  Disable expansion of the declaration language specifier
0x0060  Disable all modifiers on the 'this' type
0x0080  Disable expansion of access specifiers for members
0x0100  Disable expansion of 'throw-signatures' for functions and pointers to
        functions
0x0200  Disable expansion of 'static' or 'virtual'ness of members
0x0400  Disable expansion of Microsoft model for UDT returns
0x0800  Undecorate 32-bit decorated names
0x1000  Crack only the name for primary declaration
        return just [scope::]name.  Does expand template params
0x2000  Input is just a type encoding; compose an abstract declarator
0x8000  Disable enum/class/struct/union prefix
0x20000 Disable expansion of __ptr64 keyword

I have used the descriptions from the IDiaSymbol::get_undecoratedNameEx documentation page for the XML documentation comments.

Additionally, here are some notes describing some oddities that these constants reveal about the UNDNAME_ flag set:

• UNDNAME_TYPE_ONLY shares its value with UNDNAME_NO_ARGUMENTS which does exist in the headers, despite not representing the current behavior of the flag (unlike the former).
• UNDNAME_RESERVED1 and UNDNAME_RESERVED2 share their values with UNDNAME_NO_MS_THISTYPE and UNDNAME_NO_CV_THISTYPE respectively. I am not sure which of the two sets of names represent today's behavior, but it is interesting that undname.exe does not describe the meaning of either.
• UNDNAME_NO_SPECIAL_SYMS shares its value with UNDNAME_HAVE_PARAMETERS. No description is given for it by undname.exe and I have not determined which name is more accurate.

Maybe it would be worth opening an issue to have the C++ documentation updated to address these ambiguities?