add move_line_down_util_non_space/move_line_up_util_non_space

[zizpop]

move_line_down_util_non_space Behavior: Move the cursor to the next line under the same column. If that spot is empty, keep moving down until you find a line that isn't empty.

I ran into a tricky navigation issue while coding. When I'm inside a huge switch statement, it's hard to jump to the next case. With a move like this, I could quickly switch between similar entries at the same level. And this doesn't need a language server (LSP)—it only relies on well-formatted code.

Example: I want to jump from .value to the next state, which is .post_value.

pub fn next(self: *@This()) NextError!Token {
    state_loop: while (true) {
        switch (self.state) {
            .value => {
                switch (try self.skipWhitespaceExpectByte()) {
                    // Object, Array
                    '{' => {
                        try self.stack.push(OBJECT_MODE);
                        self.cursor += 1;
                        self.state = .object_start;
                        return .object_begin;
                    },
                    '[' => {
                        try self.stack.push(ARRAY_MODE);
                        self.cursor += 1;
                        self.state = .array_start;
                        return .array_begin;
                    },

                    // String
                    '"' => {
                        self.cursor += 1;
                        self.value_start = self.cursor;
                        self.state = .string;
                        continue :state_loop;
                    //  <.....same code.....>

this is page 1

            .post_value => {
                if (try self.skipWhitespaceCheckEnd()) return .end_of_document;

                const c = self.input[self.cursor];
                if (self.string_is_object_key) {
                    self.string_is_object_key = false;
                    switch (c) {
                        ':' => {
                            self.cursor += 1;
                            self.state = .value;
                            continue :state_loop;
                        },
                        else => return error.SyntaxError,
                    }
                }

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