Read Kit/Generator from the CMakeCache.txt

### Brief Issue Summary
I am configuring my cmake-project with conan. I am having some special profiles for different compiler.
When opening the folder and trying to use the cmake-tools, i always have to select a kit. These seem sometimes to differ. Especially when i am using platform and toolsets.
The kit/generator should be automatically selected by the already generated cmake-cache.

### Expected:

1. Having a possibility to first check in the cmake.buildDirectory, if there is already a CMakeCache.txt
2. Setting the kit, generator, toolset, platform and cmake-executable regarding the cache (using different cmake-versions in different projects)

### Platform and Versions

- **Operating System**: Windows
- **CMake Version**: 3.10 or newer
- **VSCode Version**: 1.47.3
- **CMake Tools Extension Version**: v1.4.1
- **Compiler/Toolchain**: differ

### Other Notes/Information

also having problems with intellisense and conan
Neverthelesse: Good tool by the way 😉

Start by examining how cmake.buildDirectory and CMakeCache.txt are currently handled when a folder opens and a kit is selected. Reproduce the Windows case with an existing cache, then verify that the kit, generator, toolset, platform, and CMake executable are derived from it without requiring manual selection.

Written by the indexing model from the issue text.