enable to pass switch values dynamically (#11057)

# Description
Closes: #7260 

About the change:
When we make an internalcall, and meet a `switch` (Flag.arg is None),
nushell will try to see if the switch is called like `--xyz=false` , if
that is true, `parse_long_flag` will return relative value.

# User-Facing Changes
So after the pr, the following would be possible:
```nushell
def build-imp [--push, --release] {
    echo $"Doing a build with push: ($push) and release: ($release)"
}
def build [--push, --release] {
    build-imp --push=$push --release=$release
}

build --push --release=false
build --push=false --release=true
build --push=false --release=false
build --push --release
build
```

# Tests + Formatting
Done

# After Submitting
Needs to submit a doc update, mentioned about the difference between
`def a [--x] {}` and `def a [--x: bool] {}`

crates/nu-parser/src/parser.rs

@@ -401,13 +401,31 @@ fn parse_long_flag(
                     }
                 } else {
                     // A flag with no argument
-                    (
-                        Some(Spanned {
-                            item: long_name,
-                            span: arg_span,
-                        }),
-                        None,
-                    )
+                    // It can also takes a boolean value like --x=true
+                    if split.len() > 1 {
+                        // and we also have the argument
+                        let long_name_len = long_name.len();
+                        let mut span = arg_span;
+                        span.start += long_name_len + 3; //offset by long flag and '='
+
+                        let arg = parse_value(working_set, span, &SyntaxShape::Boolean);
+
+                        (
+                            Some(Spanned {
+                                item: long_name,
+                                span: Span::new(arg_span.start, arg_span.start + long_name_len + 2),
+                            }),
+                            Some(arg),
+                        )
+                    } else {
+                        (
+                            Some(Spanned {
+                                item: long_name,
+                                span: arg_span,
+                            }),
+                            None,
+                        )
+                    }
                 }
             } else {
                 working_set.error(ParseError::UnknownFlag(

src/tests/test_custom_commands.rs

@@ -83,6 +83,35 @@ fn custom_switch2() -> TestResult {
 
 #[test]
 fn custom_switch3() -> TestResult {
+    run_test(
+        r#"def florb [ --dry-run ] { $dry_run }; florb --dry-run=false"#,
+        "false",
+    )
+}
+
+#[test]
+fn custom_switch4() -> TestResult {
+    run_test(
+        r#"def florb [ --dry-run ] { $dry_run }; florb --dry-run=true"#,
+        "true",
+    )
+}
+
+#[test]
+fn custom_switch5() -> TestResult {
+    run_test(r#"def florb [ --dry-run ] { $dry_run }; florb"#, "false")
+}
+
+#[test]
+fn custom_switch6() -> TestResult {
+    run_test(
+        r#"def florb [ --dry-run ] { $dry_run }; florb --dry-run"#,
+        "true",
+    )
+}
+
+#[test]
+fn custom_flag1() -> TestResult {
     run_test(
         r#"def florb [
             --age: int = 0
@@ -96,7 +125,7 @@ fn custom_switch3() -> TestResult {
 }
 
 #[test]
-fn custom_switch4() -> TestResult {
+fn custom_flag2() -> TestResult {
     run_test(
         r#"def florb [
             --age: int