The default value for cmake.buildTargetName is not a valid build target name

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### Brief Issue Summary

It seems impossible to create a task that will build the current target, including when a current target has not been explicitly selected. It would be convenient to have this as the default build task, such that by default it does the same as `cmake: Build`, but one can also select a different target and subsequent builds would be scoped to that target.

```json
{
"type": "cmake",
"label": "Build Selected Target",
"command": "build",
"targets": ["${command:cmake.buildTargetName}"],
"problemMatcher": "$blah",
"group": {
"kind": "build",
"isDefault": true
}
},
```

When invoking this task without having selected a build target in the CMake pane, it attempts to execute the `[Targets in Preset]` target, which is invalid, and fails. It would be more convenient for this value to default to `all`.

### CMake Tools Diagnostics

```shell
{
"os": "win32",
"vscodeVersion": "1.87.0",
"cmtVersion": "1.17.17",
"configurations": [
{
"folder": ",
"cmakeVersion": "3.28.20240123",
"configured": true,
"generator": "Ninja",
"usesPresets": true,
"compilers": {
"C": "clang",
"CXX": "clang"
}
}
],
"cpptoolsIntegration": {
"isReady": true,
"hasCodeModel": true,
"activeBuildType": "Debug",
"buildTypesSeen": [
"Debug"
],
"requests": [],
"responses": [],
"partialMatches": [],
"targetCount": 252,
"executablesCount": 6,
"librariesCount": 215,
"targets": []
},
"settings": [
{
"communicationMode": "automatic",
"useCMakePresets": "always",
"configureOnOpen": true
}
]
}
```
```

### Debug Log

```shell
* Executing task: Build Selected Target

build task started....
"C:\Program Files\CMake\bin\cmake.EXE" --build --target "[Targets In Preset]"
ninja: error: unknown target '[Targets In Preset]'
build finished with error(s).

* The terminal process failed to launch (exit code: 1).
* Terminal will be reused by tasks, press any key to close it.
```

### Additional Information

_No response_

Start by locating the implementation of the cmake.buildTargetName setting and the task target expansion used for CMake build tasks. Reproduce the task without a selected target, then verify that its default resolves to a valid target such as all and that selecting a target still scopes later builds to it.

Written by the indexing model from the issue text.