[lldb] add stop-at-user-entry option to process launch (#67019)

## Description
This pull request adds a new `stop-at-user-entry` option to LLDB
`process launch` command, allowing users to launch a process and pause
execution at the entry point of the program (for C-based languages,
`main` function).

## Motivation
This option provides a convenient way to begin debugging a program by
launching it and breaking at the desired entry point.

## Changes Made
- Added `stop-at-user-entry` option to `Options.td` and the
corresponding case in `CommandOptionsProcessLaunch.cpp` (short option is
'm')
- Implemented `GetUserEntryPointName` method in the Language plugins
available at the moment.
- Declared the `CreateBreakpointAtUserEntry` method in the Target API.
- Create Shell test for the command
`command-process-launch-user-entry.test`.

## Usage
`process launch --stop-at-user-entry` or `process launch -m` launches
the process and pauses execution at the entry point of the program.