Use Windows native path separator in ESP_SR model copy command pattern

Although Windows generally supports the use of the POSIX compliant slash path separator in addition to the Windows
native backslash separator, in the specific use case where a path is present in a native command executed via an
argument to `cmd /c` in a platform command pattern, it is mandatory to use backslash path separators.

Previously, a slash path separator was used in the `tools.esp32-arduino-libs.path` and `compiler.sdk.path` platform
properties, which were referenced in a `copy` command in the `cmd /c` argument part of the platform's
`recipe.hooks.objcopy.postobjcopy.2.pattern.windows` command pattern. This caused compilation to fail with a "The syntax
of the command is incorrect." error under the following conditions:

- The compilation is performed on a Windows machine
- The compiled sketch uses the ESP_SR library

This is fixed by adding Windows override variants of the properties, with backslash path separators.

Author: per1234

platform.txt

@@ -2,6 +2,7 @@ name=ESP32 Arduino
 version=3.0.0
 
 tools.esp32-arduino-libs.path={runtime.platform.path}/tools/esp32-arduino-libs
+tools.esp32-arduino-libs.path.windows={runtime.platform.path}\tools\esp32-arduino-libs
 tools.xtensa-esp32-elf-gcc.path={runtime.platform.path}/tools/xtensa-esp32-elf
 tools.xtensa-esp32s2-elf-gcc.path={runtime.platform.path}/tools/xtensa-esp32s2-elf
 tools.xtensa-esp32s3-elf-gcc.path={runtime.platform.path}/tools/xtensa-esp32s3-elf
@@ -30,6 +31,7 @@ compiler.path={tools.{build.tarch}-{build.target}-elf-gcc.path}/bin/
 compiler.prefix={build.tarch}-{build.target}-elf-
 
 compiler.sdk.path={tools.esp32-arduino-libs.path}/{build.mcu}
+compiler.sdk.path.windows={tools.esp32-arduino-libs.path}\{build.mcu}
 
 # EXPERIMENTAL feature: optimization flags
 #  - this is alpha and may be subject to change without notice