Parsing of nested templates is slow

[guwirth]

Previously, nested templates with >> at the end were handled via a grammar extension (N1757/Approach 3). For deeper nested templates this led to many look-ahead symbols and exponentially increasing execution time. The treatment has now been moved to the Lexer: Solving the problem amounts to decreeing that under some circumstances a >> token is treated as two right angle brackets instead of a right shift operator (N1757/Approach 1).

• add 'Right Angle Brackets N1757' document
• close Parsing of nested templates is slow: template <... template<...>> #1685

Some samples which are much faster now:

using List= TypeA<A, TypeB<B, TypeC<C, TypeD<D, TypeE<E, TypeF<F, TypeG<G, TypeH<H, I>>>>>>>>;
UARTTask<BL6523GXController<UART<UART_NUM_2, 4800, 8, 'N', 1>>> uartTask;

void f1() {
   TypeA<A, TypeB<B, TypeC<C, TypeD<D;
}

void f2() {
   TypeA<A, TypeB<B, TypeC<C, TypeD<D>>>> t;
}

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