Fix normalizing pin labels for C++ and add QuickHelp for C++ and Tabtest editors

[brusherru]

It fixes #1664
Also, it adds a new feature: QuickHelp now contains a list of inputs/outputs available in the C++ editor and in the tabtest editor. Also, it contains a link to a full reference in our docs.

[nkrkv]

A general note. I recommend to avoid mixing two concepts: pin name normalization (converting empty labels to IN1, IN2, OUT, etc) and C++ escaping (getting rid of invalid C++ chars). They should be named accordingly and used in a pipe where necessary.

[nkrkv]

Huh. One more time. The escape functions are quite generic to be unbound from the pin/project concept.

• cppEscape and unicodeCharsToUnicodeSequence should be in xod-func-tools, not in xod-project
• Changes in *.re* should reflect this as well

[nkrkv]

🐛

Steps to reproduce

1. Open xod/math/clip
2. Change the label of X to X°-§
3. Open its not-implemented-in-xod
4. Open Quick Help

Expected behavior

• The quickhelp lists the input escaped: input_XUxxxx_Uxxxx

Actual behavior

• The input is listed as X°_§ (only the hyphen is transformed)

[nkrkv]

👍 👍 👍 Now excellent

[evgenykochetkov]

LGTM