[cmake] Add helper options to flatbuffers_generate_headers()

[alexv-ds]

Description

Added helper options to flatbuffers_generate_headers()

• FILENAME_SUFFIX - adds --filename-suffix argument to flatc
• NO_FILENAME_SUFFIX - adds --filename-suffix "" (empty string) to flatc. This option exists separately from FILENAME_SUFFIX because passing an empty string became possible only in cmake 3.31.
• FILENAME_EXT - adds --filename-ext argument to flatc

Motivation

This is needed for correct cmake dependency tracking. If the corresponding parameters are added through FLAGS, cmake starts tracking a file that will never be generated. As a result, the headers are regenerated on every build.

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