Remove TactilityC and Firmware subprojects (#638)

- Removed TactilityC, moved its symbols to existing modules and several new ones (pthread-module, c-symbols-module, cpp-symbols-module, posix-symbols-module, freertos-module).
- Removed Firmware subproject and moved main() into Tactility subproject.
- Strengthened application archive, path, version, stack-size, and device validation.
- Moved symbol resolution for elf_loader to app-esp32-module.
- Improved `struct Module` declarations and made module and symbol definitions in modules more consistent.
- Removed old http download code from Tactility subproject.
- Rename app-module's source files for consistency.
- Add missing pthread symbols.
- Kernel module symbols are now resolvable on all platforms.

Modules/cpp-symbols-module/README.md

@@ -0,0 +1,62 @@
+# cpp-symbols-module
+
+Exports the C++ runtime/ABI symbols that side-loaded ELF apps need but that don't come from any
+single library header - compiler-generated helpers (`operator new`/`delete`, vtable guard
+variables) and libstdc++ internals that are normally only reachable through template
+instantiation, not a plain function call. Apps still `#include <new>`/`<map>`/`<string>` etc.
+directly; this module only makes sure the actual out-of-line definitions resolve when their ELF
+is loaded into the firmware.
+
+ESP32-only: several of these symbols are mangled for a 32-bit ABI (`j` = `unsigned int`, used
+here to represent `size_t`). On a 64-bit host those would mangle differently (e.g. `_Znwm`
+instead of `_Znwj`), so this module doesn't build for the POSIX simulator.
+
+## Supported symbols
+
+### Compiler/runtime ABI support
+
+- `operator new(unsigned int)` / `operator delete(void*, unsigned int)` (`_Znwj` / `_ZdlPvj`)
+- `std::nothrow`
+- `__cxa_pure_virtual` - called through a pure-virtual slot before a derived class's vtable is
+  fully constructed; see [Bare metal C++](https://arobenko.github.io/bare_metal_cpp/).
+- `__cxa_guard_acquire` / `__cxa_guard_release` / `__cxa_guard_abort` / `__cxa_guard_dummy` -
+  thread-safe one-time initialization of function-local `static` variables.
+
+### libstdc++ exception helpers
+
+Out-of-line `std::__throw_*` functions libstdc++ headers call instead of throwing directly, to
+keep the throw site small:
+
+- `std::__throw_bad_alloc`
+- `std::__throw_bad_array_new_length`
+- `std::__throw_bad_function_call`
+- `std::__throw_length_error`
+- `std::__throw_logic_error`
+- `std::__throw_out_of_range_fmt`
+- `std::__throw_system_error`
+
+### `std::map` / `std::set` (red-black tree internals)
+
+Non-template helpers shared by every `std::map`/`std::set` instantiation:
+
+- `std::_Rb_tree_increment` / `std::_Rb_tree_decrement`
+- `std::_Rb_tree_insert_and_rebalance`
+
+### `std::string`
+
+- `basic_string::_M_replace_cold` - the rarely-taken slow path of `std::string::replace`,
+  split out of the header-inlined fast path.
+
+## Adding a new symbol
+
+1. Find the mangled name (`nm`/`c++filt`, or the linker's "undefined reference" error from an
+   app build).
+2. Add an `extern "C"` declaration for it in `source/module.cpp` if the name isn't already a
+   valid identifier you can reference directly (mangled names usually are, e.g. `_ZSt19...`).
+3. Add a `DEFINE_MODULE_SYMBOL(...)` entry (or a manual `{ "mangled_name", (void*)&expr }` pair
+   when the address isn't reachable through the mangled identifier itself, e.g. `std::nothrow`
+   or the `__throw_*` functions).
+
+## License
+
+This module is licensed under the [Apache v2.0](LICENSE-Apache-2.0.md) license.