Merge launcher into retro-core

[ducalex]

I want retro-core to become a standalone esp32 application, containing the launcher and the core emulators. It should be buildable without rg_tool.py, with standard esp-idf tooling.

Benefits:

• retro-core can now be built and flashed with idf.py (assuming the user doesn't care about DOOM and such)
• retro-core being standalone means it can be built for platforms with no concept of partitions/multiple exes
• Reduced firmware size
• All retro-core apps can now access wifi if they want
• Faster builds because it means one less app

Drawbacks:

• It breaks git history for launcher files (but --follow mostly works around that)
• The presence of the wifi stack, even when not enabled, reserves some amount of internal memory

I've tried on several occasions to merge the launcher and retro-core (latest attempt here), but every time there are issues that stops me. And then I forget what the problem was.

This issue is meant to track problems found during testing.

[ducalex]

Currently the blocking problems are:

• Must investigate the wifi stack's usage of memory and see if it affects any emulator and if it can be reduced via menuconfig options

[ducalex]

Relevant memory info. These are the additional libraries linked in when networking is enabled:

            Archive File DRAM .data & 0.bss .rtc_noinit IRAM0 .text & 0.vectors ram_st_total Flash .text & .rodata & .rodata_noload & .appdesc flash_total
           libnet80211.a        758    6841           0           0           0         7599      105101      8875            10410          0      125144
               liblwip.a         25    3896           0           0           0         3921       77727       721                0          0       78473
         libmbedcrypto.a         36      85           0          30           0          151       67647     10760                0          0       78473
                 libpp.a       2447    1348           0        1354           0         5149       51351      3355             1465          0       59972
                libphy.a       2361     637           0        8902           0        11900       28915         0                0          0       40178
     libwpa_supplicant.a         12    1436           0           0           0         1448       39281       803                0          0       40096
            libmbedtls.a          0     200           0           0           0          200       16263      4581                0          0       20844
           libesp_wifi.a        480      35           0         390           0          905        2873       953                0          0        4696
            libesp_phy.a         16      25           0         194           0          235        1522      1081                0          0        2813

In other words the Wifi/IP/TLS stack currently reserves 31KB of internal memory even when not in use.

It goes down to 18KB when CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY=y is set:

Per-archive contributions to ELF file:
            Archive File DRAM .data & 0.bss .ext_ram.bss .rtc_noinit IRAM0 .text & 0.vectors ram_st_total Flash .text & .rodata & .rodata_noload & .appdesc flash_total
           libnet80211.a        758       0         6841           0           0           0         7599      105057      8875            10410          0      125100
               liblwip.a         17       0         2275           0           0           0         2292       54480       563                0          0       55060
         libmbedcrypto.a         36      85            0           0          30           0          151       67627     10760                0          0       78453
                 libpp.a       2447       0         1348           0        1354           0         5149       51371      3355             1465          0       59992
                libphy.a       2361     637            0           0        8902           0        11900       28907         0                0          0       40170
     libwpa_supplicant.a         12       0         1436           0           0           0         1448       39289       803                0          0       40104
            libmbedtls.a          0     200            0           0           0           0          200       16263      4581                0          0       20844
           libesp_wifi.a        480      35            0           0         390           0          905        2785       953                0          0        4608
            libesp_phy.a         16      25            0           0         194           0          235        1522      1081                0          0        2813

I've disabled this option because it prevents boot when SPIRAM can't be initialized and I wanted to be able to at least show an error on screen when that happens. But retro-go doesn't really work without SPIRAM so maybe it's time to add CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY=y back...