Add XL Keyboards XL 87 RGB

[Hiiwwy]

Description

Adds support for the XL Keyboards XL 87 RGB, a wired 87-key ANSI TKL keyboard.

Hardware and firmware details:

• APM32F103CBT6 MCU using the STM32F103-compatible QMK platform
• 16 MHz external crystal with a 72 MHz system clock
• uf2boot bootloader with the application starting at 0x08004000
• 6 x 17 switch matrix
• 91 top-side WS2812 LEDs and 32 underglow LEDs
• tkl_ansi community layout
• Embedded-flash wear-leveling EEPROM with the final 2 KB of Flash reserved by a keyboard-specific linker script
• Caps Lock and Scroll Lock indicators using their corresponding key LEDs

The VIA keymap and VIA keyboard definition will be submitted separately to the-via/qmk_userspace_via and the-via/keyboards.

Tested on the production APM32F103CBT6 hardware:

• Keyboard input and NKRO
• RGB Matrix keylight and underglow
• Caps Lock and Scroll Lock indicators
• uf2boot entry and repeated UF2 firmware updates
• EEPROM persistence across power cycles
• qmk lint -kb xl_keyboards/xl_87_rgb --strict
• Default keymap compilation
• VIA keymap compilation in external userspace
• git diff --check

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

None.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[Hiiwwy]

Thanks for the review. I have addressed the requested changes:

• Removed VIA-specific customization from the QMK keyboard code
• Removed the redundant EEPROM driver settings
• Added copyright headers
• Added QK_BOOT to the Fn layer
• Updated the README to use the standard bootloader section

The default keymap builds successfully, qmk lint --strict passes, and git diff --check is clean.

[Hiiwwy]

Hi @zvecr, all requested changes have now been addressed, including the USB VID update and moving QK_BOOT to Fn + Escape.

All CI checks are passing, and I have resolved the completed review conversations. When you have time, could you please take another look? Thanks!